bacula: allow mysqldumps to be kept locally

Should a local_dump_dir parameter be defined and mysqldump version is
using keep a dump locally in the machine in the directory defined by the
parameter. While at it create rspec rules for it

Change-Id: Ib13604d83dd2a47467da41e6d6a01f9346b211f9
Merge "bacula: allow mysqldumps to be kept locally" into production