fix Apache site setup for Bugzilla

follow-up fix to Iddc778a28163

which put the file directly into sites-enabled

the result was that we have 2 files, one in -enabled
one in -available with different content

we want proper symlinks instead

also: set priority to 10, we want to load
Bugzilla before any other site, so that clients
who don't speak SNI get the Bugtracker, and not
Arabic Planet

Change-Id: I6263aba13914627a4b60b0fbb134502993a9eda5
Merge "fix Apache site setup for Bugzilla" into production