Skip TestUnixSocket by default
Skip TestUnixSocket by default

This test requires starting an actual memcached server, takes a while to
run, and is sometimes flaky if the underlying execs don't work out.

creiht/hummingbird,troubling/hummingbird,creiht/hummingbird,redbo/hummingbird,corystone/hummingbird,redbo/hummingbird,nadeemsyed/hummingbird,troubling/hummingbird,nadeemsyed/hummingbird,corystone/hummingbird