appliance: Increase udev timeout to 6000s (RHBZ#1096579).

If the image is located on NFS, and the NFS mount is performing a
large copy, then all other NFS operations stop.  This delay can be
large enough that we hit the current 10 minute timeout in udev.

Increasing this to 100 minutes is reported to cure the problem (in
reality we want udev to wait indefinitely).