Let cap_integrity test be more expressive

By using the `compare_output_to` method from the run tool instead of using
regexp in the cap_integrity run-script, the test outputs the undesired lines
instead of just signaling that the test failed.

base/run/cap_integrity.run

@@ -32,8 +32,5 @@ match_max -d 100000
 
 run_genode_until {child exited with exit value 0.*} 60
 
-if {[regexp {\[init\] test message} $output]} {
-	exit -1
-}
-
-puts "Test succeeded"
+grep_output {\[init\] test message}
+compare_output_to { }