VirtualDomain: check process table for qemu-system-* too, not just qemu-kvm

The Qemu/KVM process name "qemu-kvm" is deprecated; qemu-system-<arch>
is now the preferred binary name. Some distributions only support the
latter. Expand the regular expression in monitor to support both names
when grepping through the process table.

Use an extended regular expression to test for both qemu-kvm
and qemu-system-*; the -E flag is specified by POSIX.