virttest.bootstrap: Suppress annoying deprecation message

In order to not get a deprecation message every
time we execute a virt test instance, let's use
a even more hackish approach to determine which
JeOS to use. We plan on dropping this and get
back to the elegant way of doing it as soon as
we get autotest 0.16 on EPEL.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>