Installer should return different exit codes for different outcomes

Currently installer tend to return 0 exit code always.

We need to be able to detect what was the outcome of installation from DT when install is launched on demand.

At very least we need to distinguish between:
   1) success
   2) user cancel
   3) generic error during installation

Please do not use -1 and 1 as error codes from installer. Those are already used by older versions of DT.
E.g. use positive codes from 10 to 1000.