lnst-ctl: Adding return value

The lnst-ctl always exited with 0. This is impractical, especially for
scripting. This commit adds return values to the lnst-ctl command that
properly reflect what happened during the execution.

Currently supported return values:
  * RETVAL_PASS = 0: When everything passed with no error
  * RETVAL_FAIL = 1: One or more tests failed
  * RETVAL_ERR  = 2: There was an error in the recipe, during the
                     matching or configuration

Signed-off-by: Radek Pazdera <rpazdera@redhat.com>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>