Add and use qemuProcessEventFree for freeing qemuProcessEvents. This
is less error-prone as the compiler can help us make sure that for
every new enumeration value of qemuProcessEventType the
qemuProcessEventFree function has to be adapted.

All process*Event functions are *only* called by
qemuProcessHandleEvent and this function does the freeing by itself
with qemuProcessEventFree. This means that an explicit freeing of
processEvent->data is no longer required in each process*Event
handler.

The effectiveness of this change is also demonstrated by the fact that
it fixes a memory leak of the panic info data in
qemuProcessHandleGuestPanic.
Reported-by: NWang Dong <dongdwdw@linux.vnet.ibm.com>
Signed-off-by: NBjoern Walk <bwalk@linux.vnet.ibm.com>
Signed-off-by: NMarc Hartmayer <mhartmay@linux.vnet.ibm.com>
Reviewed-by: NBoris Fiuczynski <fiuczy@linux.vnet.ibm.com>
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>