kola/tests/fleet: Retry unit status detection
kola/tests/fleet: Retry unit status detection

The fleet documentation claims that starting units should block
until it's active, but that is not the case.  Since fleet is slated
for removal from the OS in February 2018, just add back retry logic
that was there originally so tests aren't randomly failing.

glevand/coreos--mantle,dm0-/mantle,dm0-/mantle,glevand/coreos--mantle