Display unrecognised whole disk devices as all grey again (#788308)

Following the switch from whole_device flag to TYPE_UNPARTITIONED,
unallocated space can be found in two partition types:
    TYPE_UNALLOCATED
    TYPE_UNPARTITIONED  (only when filesystem == FS_UNALLOCATED)

As the file system in both cases is FS_UNALLOCATED check for that when
determining whether a partition is unallocated or not.

Bug 788308 - Remove whole_device partition flag