Changes

testenv: move titan_min to testsrcdir.cfg

Adjust the code so it gets titan_min= from testsrcdir.cfg, instead of
having it in testenv.cfg and enforcing that the value is the same across
all files in the same source directory.

While at it, set the default to 11.1.0 (the value that is currently in
all testenv.cfg files), so we don't need to repeat it in all source
directories.

Change-Id: Ife12e3b3294ce16ebedee1b7998d3b89856f0328