btrfs: check if mount opts are applied

btrfs: check if mount opts are applied

This new test will apply different mount points and check if they
were applied by reading /proc/self/mounts. Almost all available
btrfs options are tested here, leaving only device=, which is tested
in btrfs/125 and space_cache, tested in btrfs/131.

This test does not apply any workload after the fs is mounted, just
checks is the option was set/unset correctly.

Kernel with the following patch should pass the test:
  btrfs: reset compression level for lzo on remount

Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>