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##### SUMMARY
The "source" folder of my collection contains several files that are not directly related to the collection itself. E.g. a `.gitignore`, a `.github` folder, a `Makefile` etc.
When using `ansible-galaxy collection build <folder>`, these files are included in the generated tarball. This is especially hurtful when the source folder also contains a Python venv that I use for developing.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
ansible-galaxy

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.9.0.dev0
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/home/egolov/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /home/egolov/Devel/ansible/ansible/lib/ansible
  executable location = /home/egolov/Devel/ansible/ansible/bin/ansible
  python version = 2.7.15 (default, Oct 15 2018, 15:26:09) [GCC 8.2.1 20180801 (Red Hat 8.2.1-2)]

```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below
empty
```

##### OS / ENVIRONMENT
Fedora


##### STEPS TO REPRODUCE
Build a collection :)

##### EXPECTED RESULTS
I'd expect only collection-relevant files/folders (those that are listed in the spec/docs) to be included.


##### ADDITIONAL INFORMATION
Alternatively, a ignore file as suggested by @bcoca  in https://github.com/ansible/ansible/pull/59121/files#r304554334 could be a fix for this.

else:
            
            
            for rname in context.CLIARGS['args']:
                role = RoleRequirement.role_yaml_parse(rname.strip())
                roles_left.append(GalaxyRole(self.galaxy, self.api, **role))
        for role in roles_left:
            
            if role_file and context.CLIARGS['args'] and role.name not in context.CLIARGS['args']:
                display.vvv('Skipping role %s' % role.name)
                continue
            display.vvv('Processing role %s ' % role.name)
            
            if role.install_info is not None:
                if role.install_info['version'] != role.version or force:
                    if force:
                        display.display('- changing role %s from %s to %s' %
                                        (role.name, role.install_info['version'], role.version or "unspecified"))
                        role.remove()
                    else:
                        display.warning('- %s (%s) is already installed - use --force to change version to %s' %
                                        (role.name, role.install_info['version'], role.version or "unspecified"))
                        continue
                else:
                    if not force:
                        display.display('- %s is already installed, skipping.' % str(role))
                        continue
            try:
                installed = role.install()
            except AnsibleError as e: