Update fs_mgr tests for new fstab format and add to TEST_MAPPING

And fix a bug in the meantime, where mounts with no filesystem
specific mount options were incorrectly having an empty string in
their set of mount options.

Test: this test
Change-Id: I9b1f14d00a90f8b95a13fcecb3cfa7fe10a2f96a
2 files changed