qemu: Fix event generated for qemuDomainRevertToSnapshot (pause->run)

qemu: Fix event generated for qemuDomainRevertToSnapshot (pause->run)

A closer review of the code shows that for the transition from paused to
running which was supposed to emit the VIR_DOMAIN_EVENT_RESUMED - no event
would be generated. Rather the event is generated when going from running
to running.

Following the 'was_running' boolean shows it is set when the domain obj
is active and the domain obj state is VIR_DOMAIN_RUNNING. So rather than
using was_running to generate the RESUMED event, use !was_running