Add some tests for options in qemu.conf

Test clear_emulator_capabilities parameter in qemu.conf.

1) Change clear_emulator_capabilities in qemu.conf;
2) Restart libvirt daemon;
3) Check if libvirtd successfully started;
4) Check if qemu process capabilities changed accordingly;

Test set_process_name parameter in qemu.conf.

1) Change set_process_name in qemu.conf;
2) Restart libvirt daemon;
3) Check if libvirtd successfully started;
4) Check if qemu command line changed accordingly;

Test seccomp_sandbox parameter in qemu.conf.

1) Change seccomp_sandbox in qemu.conf;
2) Restart libvirt daemon;
3) Check if libvirtd successfully started;
4) Check if qemu command line changed accordingly;

Signed-off-by: Hao Liu <hliu@redhat.com>