inspection: Not an installer if there are multiple partitions (RHBZ#1171666).

Regular EFI disks have /EFI on the first (VFAT) partition, but they
are not installers.

Fix this by only considering something to be an installer if it has a
single partition (or whole disks like ISOs).

Implementing this is quite complex since when checking a filesystem,
we don't have information about whether we are even looking at a
partition, nor about whether it's the first partition out of how many.
The majority of the commit is changing the code to collect that
information.
arm: Use -cpu host on KVM.