VirtualDomain: add some polish for libvirtd-less functionality

The recent changes to make VirtualDomain perform `monitor`actions without a running libvirtd missed a couple of bits:

* `virsh uri` would still be called unconditionally, even when `OCF_RESKEY_hypervisor` was set. This would fail against a non-running libvirtd. Since the `OCF_RESKEY_hypervisor_default` variable is actually no longer used, this call be simplified, avoiding the superfluous `virsh uri` call.
* The check for a running Qemu/KVM process without a running libvirtd would only work if the emulator binary is called `qemu-kvm`, which is true for CentOS 6 but no longer applies to current Ubuntu and possibly other platforms. Now, this tests for `qemu-system-*` as well.