The validation functions to test for the number of passed arguments did not
pluralize `argument(s)`, and used `argument(s)` in all cases.
This patch adds a simple `pluralize()` helper to improve this.
Before this change, `argument(s)` was used in all cases:
$ docker container ls foobar
"docker container ls" accepts no argument(s).
$ docker network create one two
"docker network create" requires exactly 1 argument(s).
$ docker network connect
"docker network connect" requires exactly 2 argument(s).
$ docker volume create one two
"docker volume create" requires at most 1 argument(s).
After this change, `argument(s)` is properly singularized or plurarized:
$ docker container ls foobar
"docker container ls" accepts no arguments.
$ docker network create one two
"docker network create" requires exactly 1 argument.
$ docker network connect
"docker network connect" requires exactly 2 arguments.
$ docker volume create one two
"docker volume create" requires at most 1 argument.
Test cases were updated accordingly.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>