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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.

tar_obj = tar.extractfile(member)
    yield tar_obj
    tar_obj.close()
@contextmanager
def _display_progress():
    config_display = C.GALAXY_DISPLAY_PROGRESS
    display_wheel = sys.stdout.isatty() if config_display is None else config_display
    if not display_wheel:
        yield
        return
    def progress(display_queue, actual_display):
        actual_display.debug("Starting display_progress display thread")
        t = threading.current_thread()
        while True:
            for c in "|/-\\":
                actual_display.display(c + "\b", newline=False)
                time.sleep(0.1)
                
                while True:
                    try:
                        method, args, kwargs = display_queue.get(block=False, timeout=0.1)
                    except queue.Empty:
                        break
                    else:
                        func = getattr(actual_display, method)
                        func(*args, **kwargs)
                if getattr(t, "finish", False):
                    actual_display.debug("Received end signal for display_progress display thread")
                    return
    class DisplayThread(object):