If there is leading or trailing whitespace in a comps group name, it
will not be included in the compose and there will even be no error
message. Whitespace on module name results in a failure.
To avoid these errors, validating the variants file will now also check
that there is no whitespace in significant places, and abort the compose
if there a problem.
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>
