Added a parameter to mysql::backup to make bzip2 compression
optional. Compression is enabled by default, so current behavior
is not affected.
Rationale:
We are storing our MySQL backups on a system with deduplication.
Compression and dedup do not play well together, so it's advantagous
to be able to disable it.
No need for setting default values to class parameters and then testing
to confirm they are set to non-default values. Simply do not give them
values to begin with.
