This makes some further tweaks to make the test more stable under heavy
load. Firstly, the background job sleeps longer, and secondly, we make
up to 3 attempts run state.running instead of just the one, in case our
first attempt was too early. It also uses threading to make the job
sleep, since the method of adding a & to the command seemed to be
producing intermittent failures with returning clean JSON.
The behavior of the set union used to combine ext_nodes and top file
matches is not consistent on Python 3 (well, 3.5 at least), and this
produces flaky test results.
Since we do not change things like the state compiler in point
releases, the method used to combine the ext_nodes and top file matches
has been changed for Oxygen and is now fully deterministic. This test
will therefore be skipped for the remainder of the 2017.7 release cycle
on Python 3.
Fixes https://github.com/saltstack/salt-jenkins/issues/686.
