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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.

if not root_only or root_only == is_root):
                    display.vvv("Skipping '%s' for collection build" % to_text(b_abs_path))
                    continue
                if os.path.islink(b_abs_path):
                    b_link_target = os.path.realpath(b_abs_path)
                    if not b_link_target.startswith(b_top_level_dir):
                        display.warning("Skipping '%s' as it is a symbolic link to a directory outside the collection"
                                        % to_text(b_abs_path))
                        continue
                manifest_entry = entry_template.copy()
                manifest_entry['name'] = rel_path
                manifest_entry['ftype'] = 'dir'
                manifest['files'].append(manifest_entry)
                _walk(b_abs_path, b_top_level_dir)
            else:
                if b_item == b'galaxy.yml':
                    continue
                elif any(fnmatch.fnmatch(b_item, b_pattern) for b_pattern, root_only in b_ignore_files
                         if not root_only or root_only == is_root):
                    display.vvv("Skipping '%s' for collection build" % to_text(b_abs_path))
                    continue
                manifest_entry = entry_template.copy()
                manifest_entry['name'] = rel_path
                manifest_entry['ftype'] = 'file'
                manifest_entry['chksum_type'] = 'sha256'
                manifest_entry['chksum_sha256'] = secure_hash(b_abs_path, hash_func=sha256)
                manifest['files'].append(manifest_entry)
    _walk(b_collection_path, b_collection_path)
    return manifest
def _build_manifest(namespace, name, version, authors, readme, tags, description, license_ids, license_file,