ssh command line help incorrect

[Stuart Bishop]

'juju help ssh' is a little confused. It states 'can be either a machine id or a service name', but that should be 'or a unit name'.

$ juju help ssh
usage: juju ssh [options] <service> [<ssh args>...]
purpose: launch an ssh shell on a given unit or machine

options:
-e, --environment (= "")
    juju environment to operate in

Launch an ssh shell on the machine identified by the <service> parameter.
<service> can be either a machine id or a service name. Any extra parameters
are treated as extra parameters for the ssh command.

[Matthew Williams (mattyw)]

There's a proposal here https://codereview.appspot.com/10683043/

[Taylor Brown (taytay)]

I just got bitten by this in 1.16, but it was due to the term service used in two other contexts, so I think two other strings could be updated as well to clarify:

1) The "usage" line still reads:
usage: juju ssh [options] <service> [<ssh args>...]

The use of the word <service> lead me to think it meant <service name>
But maybe "service" means "unit or machine" in juju slang? Not sure. (I'm new)

Perhaps something like this would be better?
usage: juju ssh [options] <unit or machine> [<ssh args>...]
purpose: launch an ssh shell on a given unit or machine

2) If you don't specify a machine or unit name, the error message currently reads:
error: no service name specified

Again, leads me to believe I can specify a service name, but I can't.