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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.

import_parser = parser.add_parser('import', parents=parents, help='Import a role')
        import_parser.set_defaults(func=self.execute_import)
        import_parser.add_argument('--no-wait', dest='wait', action='store_false', default=True,
                                   help="Don't wait for import results.")
        import_parser.add_argument('--branch', dest='reference',
                                   help='The name of a branch to import. Defaults to the repository\'s default branch '
                                        '(usually master)')
        import_parser.add_argument('--role-name', dest='role_name',
                                   help='The name the role should have, if different than the repo name')
        import_parser.add_argument('--status', dest='check_status', action='store_true', default=False,
                                   help='Check the status of the most recent import request for given github_'
                                        'user/github_repo.')
    def add_setup_options(self, parser, parents=None):
        setup_parser = parser.add_parser('setup', parents=parents,
                                         help='Manage the integration between Galaxy and the given source.')
        setup_parser.set_defaults(func=self.execute_setup)
        setup_parser.add_argument('--remove', dest='remove_id', default=None,
                                  help='Remove the integration matching the provided ID value. Use --list to see '
                                       'ID values.')
        setup_parser.add_argument('--list', dest="setup_list", action='store_true', default=False,
                                  help='List all of your integrations.')
        setup_parser.add_argument('source', help='Source')
        setup_parser.add_argument('github_user', help='GitHub username')
        setup_parser.add_argument('github_repo', help='GitHub repository')
        setup_parser.add_argument('secret', help='Secret')
    def add_login_options(self, parser, parents=None):