Add environment-list command

While we're at it, I also have this command. Not sure how useful it is. I've used it a few times, and it could use some improvements, but in case it helps anyone, here it is.

ads `sc el environment_name`, a command that will list all nodes in an environment.  It optionally lets you add a -a value to specify an attribute but it's basically a wrapper for knife search node, for very, very lazy pees like yours truly.