Use "errors=remount-ro" fstab option only within supported filesystems

Also XFS doesn't support the errors=remount-ro option, but instead of
disabling the option for file systems that don't support it, let's
only enable it for the once that support it (according to linux's
source).

Thanks: Chris Hofstaedtler for the bug report
Closes: https://github.com/grml/grml-debootstrap/issues/199