Provide more information why an install failed

- Incorporate "App not installed" into error string
- Change failure_invalid string as it does not always mean corrupt
- Provide non-translated "raw" status message from package manager in
  the UI

Test: Installed Firefox 18, then tried to install Firefox 15. Saw error
message:

App not installed as package appears to be invalid
INSTALL_FAILED_VERSION_DOWNGRADE

Change-Id: Ia9fe97dda7e683d5446d48710ed2ee859c6b04d6
Fixes: 29343425