[apt key] Fixup breakage from apt key installation logic change

[mikaelarguedas]

Follow-up of: #114

• The snapshots repositories dont have a deb for keys yet so the original logic should be used for snapshots
• The version number should evaluated at template generation time: this way we can break docker cache when the version changes
• Test:
  • If it works fine for the testing repo
  • (low priority) If it works on the ros1_bridge image generation

[mikaelarguedas]

Closed by #116