Use /info to check if SLO is enabled

The functional tests have some hokey detection of SLO support that
pre-dates the /info API, but we can do better now.

Also moved the SLO check up inside the setUp method so that skipping
the SLO tests should be somewhat faster now.

Change-Id: I645718b459d794a9a97770f7162934558c94f3e8
Merge "Use /info to check if SLO is enabled"