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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.

co.GlobalCLIArgs._Singleton__instance = None
    yield
    co.GlobalCLIArgs._Singleton__instance = None
@pytest.fixture()
def collection_input(tmp_path_factory):
    ''' Creates a collection skeleton directory for build tests '''
    test_dir = to_text(tmp_path_factory.mktemp('test-ÅÑŚÌβŁÈ Collections Input'))
    namespace = 'ansible_namespace'
    collection = 'collection'
    skeleton = os.path.join(os.path.dirname(os.path.split(__file__)[0]), 'cli', 'test_data', 'collection_skeleton')
    galaxy_args = ['ansible-galaxy', 'collection', 'init', '%s.%s' % (namespace, collection),
                   '-c', '--init-path', test_dir, '--collection-skeleton', skeleton]
    GalaxyCLI(args=galaxy_args).run()
    collection_dir = os.path.join(test_dir, namespace, collection)
    output_dir = to_text(tmp_path_factory.mktemp('test-ÅÑŚÌβŁÈ Collections Output'))
    return collection_dir, output_dir
@pytest.fixture()
def collection_artifact(monkeypatch, tmp_path_factory):