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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.

from ansible.utils.collection_loader import AnsibleCollectionRef
from ansible.utils.display import Display
from ansible.utils.hashing import secure_hash, secure_hash_s
from ansible.module_utils.urls import open_url
urlparse = six.moves.urllib.parse.urlparse
urllib_error = six.moves.urllib.error
display = Display()
MANIFEST_FORMAT = 1
class CollectionRequirement:
    _FILE_MAPPING = [(b'MANIFEST.json', 'manifest_file'), (b'FILES.json', 'files_file')]
    def __init__(self, namespace, name, b_path, api, versions, requirement, force, parent=None, metadata=None,
                 files=None, skip=False):
        """
        Represents a collection requirement, the versions that are available to be installed as well as any
        dependencies the collection has.
        :param namespace: The collection namespace.
        :param name: The collection name.
        :param b_path: Byte str of the path to the collection tarball if it has already been downloaded.
        :param api: The GalaxyAPI to use if the collection is from Galaxy.
        :param versions: A list of versions of the collection that are available.
        :param requirement: The version requirement string used to verify the list of versions fit the requirements.
        :param force: Whether the force flag applied to the collection.
        :param parent: The name of the parent the collection is a dependency of.
        :param metadata: The galaxy.api.CollectionVersionMetadata that has already been retrieved from the Galaxy
            server.
        :param files: The files that exist inside the collection. This is based on the FILES.json file inside the
            collection artifact.
        :param skip: Whether to skip installing the collection. Should be set if the collection is already installed
            and force is not set.
        """