virttest/qemu_monitor.py: Allow '=' in parameter string for HMP

Pull request #818 introduced a possibility to have "=" chars in parameters of send_args_cmd() method in HMP/QMP monitor.
But the code of parsing such parametres with "=" was added only to QMPMonitor and not to HumanMonitor class which causes SSL Spice migration with qemu monitor parameter "C=CZ/L=BRNO/O=SPICE/CN=my Server" to fail since obviously It uses HumanMonitor, instead of QMP Monitor (whatever the difference is).

Signed-off-by: Marian Krcmarik <mkrcmari@redhat.com>