Fix initialized memory error reported by Valgrind. Disable 2 tests that produce memory leaks due to a bug in g++.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Use '--track-origins=yes' option in valgrind
Use suppressions file to ignore certain valgrind warnings
Update memcheck.supp

add reference for the suppression stuff
[skip ci]
Add "-VV" option to MemCheck to avoid travis time-outs