feat(corectl): Run command if provided to corectl ssh
Merge pull request #74 from bcwaldon/ssh-arg

feat(corectl): Run command if provided to corectl ssh
feat(corectl): Shorten machine names; lengthen with -l
feat(corectl): print hyphens for no-data in list-machines
feat(corectl): present machine IP in list-units

The IP of the Machine to which a unit was scheduled is
appended to that Machine's name in the list-units output.
feat(corectl): Allow machine lookup by prefix in corectl-ssh