restore formal call to sys.exit() in top-level main; this is needed

for companion testing collateral which expects SystemExit exceptions
to be raised.

Signed-off-by: Karl W Schulz <karl.schulz@amd.com>

src/omniperf

@@ -24,6 +24,7 @@
 # SOFTWARE.
 ##############################################################################el
 
+import sys
 from omniperf_base import Omniperf
 
 def main():
@@ -43,5 +44,7 @@ def main():
     else:
         omniperf.error("Unsupported execution mode")
 
+    sys.exit(0)
+
 if __name__ == "__main__":
     main()