fix the mount.mounted opts default value behavior

the string "defaults" is useful when mounting a volume but doesn't show
up in the options of already-mounted volumes, so filter it out when
determining whether options have changed and we should therefore
remount.

my volume was remounting every time until I made this fix, simply because I wasn't specifying any options myself.
yes, this is the important change. I probably shouldn't have been mixing changes together.