fix the test suites

ezmq connect and bind calls in the ezmq_zmq2 test suite have changed,
add 60 second timeouts for all test cases.
update travis config

run travis with an extra rebar.config to pull in erl_zmq2 for interop
tests.
libzmq2 compatible decoding of the greeting

ZeroMQ RFC 13 says IDFlags should be 0x00 in the greeting, however the actual
libzmq2 implementation sends 0x7E, so only insist on the LSB beeing zero.