Use travis for OSX tests

@kali and @meskio agreed that travis OSX tests would be nice until we have a proper solution.

I already pushed a very basic travis_osx_builds to leap/bitmask-dev, and configured travis to run osx tests here: https://travis-ci.org/leapcode/bitmask-dev

They currently fail with

clang -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -Qunused-arguments -I/usr/local/include/sqlcipher -DMODULE_NAME="pysqlcipher.dbapi2" -DSQLITE_ENABLE_FTS3=1 -DSQLITE_ENABLE_FTS5=1 -DSQLITE_ENABLE_RTREE=1 -DSQLITE_ENABLE_LOAD_EXTENSION=1 -DSQLITE_HAS_CODEC=1 -DSQLITE_TEMP_STORE=2 -DHAVE_USLEEP=1 -Iamalgamation -I/usr/local/Cellar/python/2.7.12_1/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c amalgamation/sqlite3.c -o build/temp.macosx-10.11-x86_64-2.7/amalgamation/sqlite3.o
    amalgamation/sqlite3.c:20258:10: fatal error: 'openssl/rand.h' file not found