Pass Python debug and job messages as literals.

We don't want the Jmsg and Dmsg calls to expand the data that it
gets passed in from a plugin. So we pass it now using a simple '%s'
format and just print the whole buffer.
Check for encryption before loading key

Now we check if we need an encryption key
before we try to get it.

Fixes #338: bls always fails when scsicrypto-sd plugin is loaded

Signed-off-by: Marco van Wieringen <marco.van.wieringen@bareos.com>