xfs: allow setting errortags at mount time

xfs: allow setting errortags at mount time

Add an errortag mount option that enables an errortag with the default
injection frequency.  This allows injecting errors into the mount
process instead of just on live file systems, and thus test mount
error handling.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>