fs_mgr: libfstab: allow recovery.fstab with suffix

Some platforms may need different fstab configs.
Accordingly, allow recovery init to select
a recovery.fstab with a suffix provided through
bootconfigs or cmdline during runtime,
to make a single recovery.img work on different
environments.

Change-Id: I0c2f61ffe9ddeb03afc54d8acc43b4917d65b846