Make sure ipa-client-install returns correct error code

https://fedorahosted.org/freeipa/ticket/1937

ipa-client/ipa-install/ipa-client-install

@@ -1193,6 +1193,8 @@ def main():
             options.unattended = True
             uninstall(options, env, quiet=True)
 
+    return rval
+
 try:
     if __name__ == "__main__":
         sys.exit(main())