make the option to fail if no output optional

different codes have different ways of doing output, so this
should be generalized in the future if we want it always on

regtest.py

@@ -1209,7 +1209,7 @@ def test_suite(argv):
                         except OSError:
                             suite.log.warn(f"unable to remove {pfile}")
 
-        if (match_count == 0):
+        if suite.fail_on_no_output and match_count == 0:
             suite.log.fail("ERROR: test output could not be found!")
 
 

suite.py

@@ -494,6 +494,9 @@ def __init__(self, args):
         # For setting a specific version of cmake
         self.cmake = "cmake"
 
+        # do we fail if there is no output?
+        self.fail_on_no_output = 0
+
     @property
     def timing_default(self):
         """ Determines the format of the wallclock history JSON file """