Fixes GB#621001: don't allow whitespaces in UUIDs
Fixes GB#621001: don't allow whitespaces in UUIDs

* Using MD5 of the mount name for the UUID of optical media
* Using MD5 of the mount path for the UUID of GMounts without
a corresponding GVolume

hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker