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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.

''' Creates a temporary tar file for _extract_tar_file tests '''
    filename = u'ÅÑŚÌβŁÈ'
    temp_dir = to_bytes(tmp_path_factory.mktemp('test-%s Collections' % to_native(filename)))
    tar_file = os.path.join(temp_dir, to_bytes('%s.tar.gz' % filename))
    data = os.urandom(8)
    with tarfile.open(tar_file, 'w:gz') as tfile:
        b_io = BytesIO(data)
        tar_info = tarfile.TarInfo(filename)
        tar_info.size = len(data)
        tar_info.mode = 0o0644
        tfile.addfile(tarinfo=tar_info, fileobj=b_io)
    sha256_hash = sha256()
    sha256_hash.update(data)
    with tarfile.open(tar_file, 'r') as tfile:
        yield temp_dir, tfile, filename, sha256_hash.hexdigest()
@pytest.fixture()
def galaxy_server():
    context.CLIARGS._store = {'ignore_certs': False}
    galaxy_api = api.GalaxyAPI(None, 'test_server', 'https://galaxy.ansible.com',
                               token=token.GalaxyToken(token='key'))
    return galaxy_api
def test_build_collection_no_galaxy_yaml():
    fake_path = u'/fake/ÅÑŚÌβŁÈ/path'
    expected = to_native("The collection galaxy.yml path '%s/galaxy.yml' does not exist." % fake_path)
    with pytest.raises(AnsibleError, match=expected):
        collection.build_collection(fake_path, 'output', False)
def test_build_existing_output_file(collection_input):