qemuMonitorJSONSendKey declares the "holdtime" argument as unsigned int
while the command was constructed in qemuMonitorJSONMakeCommand using
the "P" modifier which took a unsigned long from the variable
arguments which then made it possible to access uninitialized memory.

This broke the qemumonitorjsontest on 32bit fedora 20:
64) qemuMonitorJSONSendKey
... libvirt: QEMU Driver error : internal error: unsupported data type 'W' for arg 'WVSƒì ‹D$0è‘wÿÿÃAå' FAILED

Uncovered by upstream commit f744b831.

Additionally add test for the hold-time option.