Useful information like Samba logging is printed to stderr. We would
like to have this information even in the successful runs of the script.

It also adds value to print both stdout and stderr even in the failing
case.

We can leverage Samba's logging system to get a better understanding as
to what's going on during the lifetime of the autoenroll script.

Mock has to be wrangled a bit to satisfy the actual `lp` object.

In case certmonger or the cepces library are not installed we do not
want to fail hard. Check for the existence of the binaries instead of
debs to be more future-proof given that cepces is not yet packaged in
Ubuntu.

Fixes UDENG-1156

In case the binaries needed for certificate autoenrollment are not
present on the system, avoid creating the needed directories.

Also add a test to illustrate that we will not fail if the directory
structure is wonky, if certmonger is not present.