qemu.tests: Add flags for add_flag test

Some flags need to be added depends on the host type for the add_flag
test of boot_cpu_model.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests: Correct the timeoout type to float

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests.cfg: Update main monitor in qmp_basic test

As this case define the monitors with its owner name. Need also
update the main_monitor to fit the monitor name change. Otherwise
function monitor() in qemu_vm will return None.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests.cfg: Use image_snapshot for enable snapshot for each guest

Use image_snapshot = yes to cfg file instead of set extra_params. To ignore
the problem that this parameter is set to no in other cfg files which will
corrupte the image.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Merge pull request #1139 from ypu/bugfix1

Some small bug fix for qemu tests  1