Offline related updates

 * Unfify offline content variable
   Collect all data in 'default_local_mirrror_content'
   variable would allow to extend default set in future
   w\o removing|renaming original one
   - add git mirror list
 * Add amphora image for pike|queens
 * debmirror:ubuntu
   - add requirment for dogtag
 * Misc:
   remove duplicate in defaults - linux_system_repo_url

Prod-related: PROD-26662 (PROD:26662)
Bug-fix: PROD-26807 (PROD:26807)

Change-Id: I77f0a3648a0a74f70d29ba388e194c51725744f0
5 files changed