[INTERNAL] removed checkSarosSupport from DiscoveryManager

The DiscoveryManager should be generic as possible. Replaced
checkSarosSupport with new queryFeature method which can be run in the
background if needed.

MISC: replaced presence.isAvailable || presence.isAway with
presence.isAvailable as this will return the same result.


Change-Id: I36c0627f5e0292291dd56aa7bf790708238f4d9a
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1159
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>