mountlist: don't use libmount to decide on dummy/remote
* lib/mountlist.c (read_file_system_list): Don't use the libmount
routines to determine whether a file system is dummy or remote,
as they're not currently compatible. For example the remoteness
is determined on file system type (for which the list seems incomplete),
rather than simply checking for a ':' in the device name.
Also libmount currently determines that 'tmpfs' is a dummy file system
even though it has associated storage.