add support for TEST_HOSTALIASES, TEST_USE_BASENAME
By default, `standard-inventory-qcow2` will use the full path and filename of
the image.qcow2 file as the host key in the inventory. If you would rather
provide a different name for the host that corresponds to the file, you can use
either the `--hostalias` cli flag or the `TEST_HOSTALIASES` environment
variable.
If you want all images to use the image basename as the hostalias,
use `--use-basename` or `TEST_USE_BASENAME=true`.