<!--- 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.

''' searches for roles on the Ansible Galaxy server'''
        page_size = 1000
        search = None
        if context.CLIARGS['args']:
            search = '+'.join(context.CLIARGS['args'])
        if not search and not context.CLIARGS['platforms'] and not context.CLIARGS['galaxy_tags'] and not context.CLIARGS['author']:
            raise AnsibleError("Invalid query. At least one search term, platform, galaxy tag or author must be provided.")
        response = self.api.search_roles(search, platforms=context.CLIARGS['platforms'],
                                         tags=context.CLIARGS['galaxy_tags'], author=context.CLIARGS['author'], page_size=page_size)
        if response['count'] == 0:
            display.display("No roles match your search.", color=C.COLOR_ERROR)
            return True
        data = [u'']
        if response['count'] > page_size:
            data.append(u"Found %d roles matching your search. Showing first %s." % (response['count'], page_size))
        else:
            data.append(u"Found %d roles matching your search:" % response['count'])
        max_len = []
        for role in response['results']:
            max_len.append(len(role['username'] + '.' + role['name']))
        name_len = max(max_len)
        format_str = u" %%-%ds %%s" % name_len
        data.append(u'')