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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.

actual = collection._get_galaxy_yml(galaxy_yml)
    assert actual['namespace'] == 'namespace'
    assert actual['name'] == 'collection'
    assert actual['authors'] == ['Jordan']
    assert actual['version'] == '0.1.0'
    assert actual['readme'] == 'README.md'
    assert actual['description'] is None
    assert actual['repository'] is None
    assert actual['documentation'] is None
    assert actual['homepage'] is None
    assert actual['issues'] is None
    assert actual['tags'] == []
    assert actual['dependencies'] == {}
    assert actual['license_ids'] == []
@pytest.mark.parametrize('galaxy_yml', [(b"""
namespace: namespace
name: collection
authors: Jordan
version: 0.1.0
readme: README.md
license: MIT"""), (b"""
namespace: namespace
name: collection
authors: Jordan
version: 0.1.0
readme: README.md
license:
- MIT""")], indirect=True)
def test_galaxy_yml_list_value(galaxy_yml):