f2fs/015: Fix mount syntax for disabling jquota

f2fs/015: Fix mount syntax for disabling jquota

F2FS has removed the trailing "=" in the mount options for disabling
user, group, and project journaled quotas. To maintain compatibility,
update the test cases in f2fs/015 to try the new syntax first, and fall
back to the legacy syntax if the initial mount attempt fails.

Signed-off-by: Joanne Chang <joannechien@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>