Exit successfully in init script if openafs isn't in modules.dep

Exit successfully in init script if openafs isn't in modules.dep

If the openafs module isn't listed in modules.dep, exit with a zero
status from the init script even if modprobe fails.  Otherwise, if a
module package and openafs-client are installed at the same time and
openafs-client is set up before the module package, the init script can
find the module, fail the modprobe (because the dependency map hasn't
yet been updated), and fail the whole installation.  Exiting with a zero
status still doesn't get OpenAFS started, but at least it doesn't leave
the system in a partly installed state.  Thanks to Durk Strooisma for the
analysis.

Closes: #486816