Move code that appends ":default" to runtime name value to CLI

After speaking with Carlos about the logic we have in our code to allow simple names for the runtime key's values (e.g., where if we see "python" we map it to "python:default"), we agreed that this friendly feature would be good to have in the base CLI instead.

As every language runtime should support the ":default" extension and, in turn, map to the runtime that had "default: true" indicated in https://github.com/apache/incubator-openwhisk/blob/master/ansible/group_vars/all.