Improve error messages in client commands.

When a client command fails due to an error in an API call,
it used to log whatever messages came back in the reply from the server,
and then generate a message saying "... see log for details".

This change improves that behavior. Now, an error message is generated
saying something like "Command failed due to error reported by server",
followed by a group of indented lines containing the messages from the
server. For example, a new error message would look like:

	Server reported error restarting job west/bozo/test/hello
	    Job 'west/bozo/test/hello' not found.

Bugs closed: aurora-771

Reviewed at https://reviews.apache.org/r/26881/