Assert installer succeeded

If the installer failed, there's no point to continue. Since Foreman 3.8
it provides exactly which steps failed which is preferred over "parsing"
the log file.

Having an assertion in a fixture should result in the the test showing
up as ERROR.

Link: https://medium.com/opsops/pytest-fail-in-a-fixture-and-in-a-test-2122fab0564
Link: theforeman/foreman-installer@0d2fb67

pytest_fixtures/core/sat_cap_factory.py

@@ -385,7 +385,7 @@ def installer_satellite(request):
 
     sat.install_satellite_or_capsule_package()
     # Install Satellite
-    sat.execute(
+    installer_result = sat.execute(
         InstallerCommand(
             installer_args=[
                 'scenario satellite',
@@ -394,6 +394,9 @@ def installer_satellite(request):
         ).get_command(),
         timeout='30m',
     )
+    # exit code 0 means no changes, 2 means changes were applied succesfully
+    assert installer_result.status in (0, 2), installer_result.stdout
+
     sat.enable_satellite_ipv6_http_proxy()
     if 'sanity' in request.config.option.markexpr:
         configure_nailgun()