Make CI use multiple tapes, not just one

Adjust tape number and size on CI machines to test with more than one mount.

[root@ctadev12 ~]# grep CAPACITY -B 1 /etc/mhvtl/mhvtl.conf
# Default media capacity in Mb
CAPACITY=1000

We write 10k 15kB files, tape size of 50MB should be far sufficient and will permit to use 3 tapes at least and test if after hitting the end of the tape all jobs are correctly rescheduled.