qemu.tests: add enable s3/s4 params for qemu_guest_agent.cfg

since miss the enable s3/s4 params when create the qemu-kvm command
for qemu_guest_agent..check_suspend test.

Signed-off-by: Shuping Cui <scui@redhat.com>
Merge pull request #1124 from spcui/qemu_guest_agent

qemu.tests: add enable s3/s4 params for qemu_guest_agent.cfg