List tests repairs and adds named variants for subtests and type specific tests.

Repairs incompatibility with standard control file and ./run.
Repairs libguestfs configuration.

virt: Adds subtests variants name.
virt: Allows filter only subtests specific for test type.
virt: Adds qemu_img and bridge_mode process to general_options.
virt: Fix test directory tag name.
virt: Fix libguestfs test.cfg to be able be started with ./run
virt: Adds cart config variant name to file mapping.
virt: Improves list tests function.
virt: Makes ./run list-test and others list test function less verbose.