init-rbdmap: Rewrite to use logger + clean-up

init-rbdmap: Rewrite to use logger + clean-up

This patch rewrites the init-rbdmap init script so that it uses logger
instead of the log_* functions. The patch also fixes various smaller
bugs like:
* MAP_RV was undefined if mapping already existed
* UMNT_RV and UMAP_RV were almost always empty (if they succeeded) ->
  removed them
* use of continue instead RET_OP in various places (RET_OP was not being
  checked after the switch to logger messages)
* removed use of DESC (used only twice and only one occurrence actually
  made sense)

Signed-off-by: Boris Ranto <branto@redhat.com>
(cherry picked from commit c567341e98fffbe39177f951511a7698f88abf5f)