Enable created_at/updated_at for port-show/chassis-show

Add new shell unitttest files in this patch to cover these new fields

Change-Id: I1af25ac8ba1263aafd6c842f26dedb303321bbb9
Partial-Bug: #1244107
Add missing i18n support

There are some exception messages in common/utils.py and shell.py that
does not support i18n, this patch update the code to support it.

Change-Id: I836b892075333d48e4d1591986fec1362c84fc61
Partial-bug: #1240402