<!--- Verify first that your issue is not already reported on GitHub -->
<!--- Also test if the latest release and devel branch are affected too -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### 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.

remove_parser = parser.add_parser('remove', parents=parents, help='Delete roles from roles_path.')
        remove_parser.set_defaults(func=self.execute_remove)
        remove_parser.add_argument('args', help='Role(s)', metavar='role', nargs='+')
    def add_delete_options(self, parser, parents=None):
        delete_parser = parser.add_parser('delete', parents=parents,
                                          help='Removes the role from Galaxy. It does not remove or alter the actual '
                                               'GitHub repository.')
        delete_parser.set_defaults(func=self.execute_delete)
    def add_list_options(self, parser, parents=None):
        list_parser = parser.add_parser('list', parents=parents,
                                        help='Show the name and version of each role installed in the roles_path.')
        list_parser.set_defaults(func=self.execute_list)
        list_parser.add_argument('role', help='Role', nargs='?', metavar='role')
    def add_search_options(self, parser, parents=None):
        search_parser = parser.add_parser('search', parents=parents,
                                          help='Search the Galaxy database by tags, platforms, author and multiple '
                                               'keywords.')
        search_parser.set_defaults(func=self.execute_search)
        search_parser.add_argument('--platforms', dest='platforms', help='list of OS platforms to filter by')
        search_parser.add_argument('--galaxy-tags', dest='galaxy_tags', help='list of galaxy tags to filter by')
        search_parser.add_argument('--author', dest='author', help='GitHub username')
        search_parser.add_argument('args', help='Search terms', metavar='searchterm', nargs='*')
    def add_import_options(self, parser, parents=None):