cmd/juju{c,d,}: fix testing issues by using package main
This issue has been biting roger and I for a while. After spending
some time on it today and looking at other examples from the std lib
of testing main packages, it looks like when testing main (ie, from cmd/go)
all the tests run in package main. Our use of main_test appears unique.
R=fwereade, niemeyer
CC=
https://codereview.appspot.com/6260054