Fixes #276 (Incorrect error handling and [help] for 'model add' using CLI)

The changes in this commit add some additional checks the syntax of the options
that are included as part of the 'model add' command; should now catch situations
where an odd number of parameters were passed in (making it impossible to
map these arguments into a Hash map that can be used to determine if an image
UUID is required for the given model template).
Adds command help text to error output for the two errors we're throwing
missed a variable when packaging the repeated code as a method
Merge pull request #277 from tjmcs/tb/fix-odd-num-args-for-hash

Fixes #276 (Incorrect error handling and [help] for 'model add')