roomservice.py: Use list type for filter() results

A filter() call returns an iterable in python3.
If len(matches) is then checked, you get a nasty error:

[...]
WARNING: Trying to fetch a device that's already there
[...]
  File "vendor/omni/build/tools/roomservice.py", line 56, in check_repo_exists
    if len(matches) != 1:
TypeError: object of type 'filter' has no len()

Change-Id: I48b42e6931bdbc1bfef2203ede0b3dadc8582a56
1 file changed