shepherd: make error message for service not found 'smarter'

This is the current displayed variant:

[user@abyayala ~]$ sudo herd ntpd stop [3/3]

Password:

herd: service 'stop' could not be found

[user@abyayala ~]$ sudo herd stop ntpd

Service ntpd has been stopped.

**

A good solution could be to display the usage of the herd stop $foo.

~~

sudo herd ntpd stop

herd: service 'stop' could not be found.

Did you mean 'herd stop foo'?

~~

or have it display the $foo which was used.

severity 26252 wishlist

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