libparted: fail (don't just warn) upon failure to inform kernel of...

libparted: fail (don't just warn) upon failure to inform kernel of...

partition change(s).
* libparted/arch/linux.c (_disk_sync_part_table): Throw an error, not
merely a warning.  When this fails, it indicates that the kernel has
not been informed, and that must translate to an error, since doing
otherwise would violate the contract of ped_disk_commit_to_os.
Suggested by Hans De Goede.