Allow team assignment when creating a user with fhc

What
Allow team assignment when creating a user with fhc

Why
To create a user in a certain team, it currently requires 2 separate fhc calls.

• fhc admin-users create (create user)
• fhc admin teams adduser (add user to team)
  A discussion in the rh-mobile-consulting Slack channel concluded that it would be useful to be able to do these 2 things in 1 command.
  It currently is possible through the UI, and looking at the API call concluded that with the right argument type, it should be possible with fhc too.

How

• Allow specifying an array of teams when creating a user
  • This will likely need changes where args are parsed to allow an array of teams https://github.com/feedhenry/fh-fhc/blob/master/lib/cmd/common/admin-users.js#L95
• Update the help docs for this command to inlcude the new arg, and an example of how to use it