When I attempt to upload a function to my Localstack instance where the runtime is specified as `provided` aka custom runtime

https://docs.aws.amazon.com/lambda/latest/dg/runtimes-custom.html


> To use a custom runtime, set your function's runtime to provided.
> ...
> If there's a file named `bootstrap` in your deployment package, Lambda executes that file. If not, Lambda looks for a runtime in the function's layers. If the bootstrap file isn't found or isn't executable, your function returns an error upon invocation.


So here's what's happening, when I upload the function to Localstack I get a Boto error:

```
File "/opt/code/localstack/localstack/services/cloudformation/cloudformation_starter.py", line 173, in parse_and_create_resource
localstack_1  |     return _parse_and_create_resource(logical_id, resource_json, resources_map, region_name)
localstack_1  |   File "/opt/code/localstack/localstack/services/cloudformation/cloudformation_starter.py", line 260, in _parse_and_create_resource
localstack_1  |     result = deploy_func(logical_id, resource_wrapped, stack_name=stack_name)
localstack_1  |   File "/opt/code/localstack/localstack/utils/cloudformation/template_deployer.py", line 715, in deploy_resource
localstack_1  |     result = deploy_resource_via_sdk_function(resource_id, resources, resource_type, func, stack_name)
localstack_1  |   File "/opt/code/localstack/localstack/utils/cloudformation/template_deployer.py", line 785, in deploy_resource_via_sdk_function
localstack_1  |     raise e
localstack_1  |   File "/opt/code/localstack/localstack/utils/cloudformation/template_deployer.py", line 782, in deploy_resource_via_sdk_function
localstack_1  |     result = function(**params)
localstack_1  |   File "/opt/code/localstack/.venv/lib/python3.7/site-packages/botocore/client.py", line 272, in _api_call
localstack_1  |     return self._make_api_call(operation_name, kwargs)
localstack_1  |   File "/opt/code/localstack/.venv/lib/python3.7/site-packages/botocore/client.py", line 576, in _make_api_call
localstack_1  |     raise error_class(parsed_response, operation_name)
localstack_1  | botocore.exceptions.ClientError: An error occurred (ValidationError) when calling the CreateFunction operation: Unable to find handler script 
```

The last item in this stack trace is the issue:

> botocore.exceptions.ClientError: An error occurred (ValidationError) when calling the CreateFunction operation: Unable to find handler script 

So it looks like it searching for `myHandler.sh` where it's appending that `.sh` or something is and that file doesn't exist so it's dying.

Per the amazon docs it should just be looking for a file name `bootstrap` if the lambda runtime is set to `provided`.

Now it's entirely possible this is an issue in Boto, but jumping to line **576** per the stack trace in the Boto source shows it's just emitting the http error, which leads me to think it's in Localstack .

**... Later ...**

Ok upon further inspection it looks like this if the offending line:

https://github.com/localstack/localstack/blob/master/localstack/services/awslambda/lambda_api.py#L420-L421

It's explicitly affixing that `.sh` extension. May AWS changed things around around how they handle "bootstrap" and at some point it in the past it was "bootstrap.sh" I dunno.. Regardless, I'm thinking the solve, which I will submit if agreed upon, is that for a `runtime` type of `provided` it should be searching for `bootstrap`  no extension at all.  I don't even know that it needs to set the handler at all.. Maybe it does for Localstack.


:return: A String[] localstack docker container names for each function.
        """
        with self.docker_container_lock:
            LOG.debug('Getting all lambda containers names.')
            cmd = '%s ps -a --filter="name=localstack_lambda_*" --format "{{.Names}}"' % self._docker_cmd()
            LOG.debug(cmd)
            cmd_result = run(cmd, asynchronous=False, stderr=subprocess.PIPE, outfile=subprocess.PIPE).strip()
            if len(cmd_result) > 0:
                container_names = cmd_result.split('\n')
            else:
                container_names = []
            return container_names
    def destroy_existing_docker_containers(self):
        """
        Stops and/or removes all lambda docker containers for localstack.
        :return: None
        """
        with self.docker_container_lock:
            container_names = self.get_all_container_names()
            LOG.debug('Removing %d containers.' % len(container_names))
            for container_name in container_names:
                cmd = '%s rm -f %s' % (self._docker_cmd(), container_name)
                LOG.debug(cmd)
                run(cmd, asynchronous=False, stderr=subprocess.PIPE, outfile=subprocess.PIPE)
    def get_docker_container_status(self, func_arn):
        """
        Determine the status of a docker container.
        :param func_arn: The ARN of the lambda function.
        :return: 1 If the container is running,
        -1 if the container exists but is not running