Mimic javac's -Werror behavior. Report warnings as warnings but if
-fainOnWarning argument is given and there are warnings return false
from Main.compile or exit with -1.
In case there are warnings and the argument is passed print "error:
warnings found and -failOnWarning specified" at the end to make it clear
to users why the build failed.

Change-Id: Id7268746ed29481a20dd6d295134dcd5db7ce437
Signed-off-by: Alexander Kurtakov <akurtako@redhat.com>