tests: Move away from landing.quilt.io
tests: Move away from landing.quilt.io

The landing pages moved to quilt.io from landing.quilt.io so the
outbound public test started failing.  Also, it seems that the quilt
tests should use more reliable website to verify network connectivity.
Thus this patch has the test access github.com -- monitoring of
quilt.io can be handled separately.

quilt/tester,kklin/tester,kklin/tester