virt: Allows filter only subtests specific for test type.

Test type: qemu, libvirt, openvswitch, libguestfs.
Adds parameter "--type-specific" to command run.
By adding this parameter run filter only type specific subtests for
list and for running the tests.

Signed-off-by: Jiří Župka <jzupka@redhat.com>
virt: Adds qemu_img and bridge_mode process to general_options.

qemu_img is necessary for some libvirt and libguestfs tests.
bridge_mode is necessary for some libvirt and libguestfs tests too.

Signed-off-by: Jiří Župka <jzupka@redhat.com>