Disable interactive mode if stdin is not available
Disable interactive mode if stdin is not available

Previously an exception would be thrown if stdin was not available at
startup. This change allows tick-cluster to continue albeit with
interactive commands disabled.

This change allows tick-cluster to be spawned in the background for
tests.

uber/ringpop-node,esatterwhite/skyring,esatterwhite/skyring,uber/ringpop,uber/ringpop-node,uber-node/ringpop-node,uber-node/ringpop-node