test: Work around sles bug

Sles' automake doesn't like including directories as extra dist -
distcheck ends up with incorrect permissions. A glob works just as well,
and we really, really don't need to ship an empty gitignore just to
create a directory we will never use.

Change-Id: Ib75a9916e93b8ca5a8e5e4b2ecdb49f2e7055b44
Signed-off-by: Robin Sonefors <robin.sonefors@op5.com>