standalone_test: Strip names in all occasions

I couldn't figure out how to automagically strip
test names in all occasions, but now we have a way:
find where is the guest name, and strip all the full
name until the guest name.

This technique is simple, effective and performing
(current guest name dict size is about 96 elements
in size), so let's go with it.
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>