scripts: runner: core: don't print unless self.debug

Guard a pair of stray printlines with "if self.debug:", so they don't
happen by default.

Signed-off-by: Marti Bolivar <marti@opensourcefoundries.com>
diff --git a/scripts/support/runner/core.py b/scripts/support/runner/core.py
index 7211006..9d5ca65 100644
--- a/scripts/support/runner/core.py
+++ b/scripts/support/runner/core.py
@@ -438,7 +438,8 @@
         try:
             subprocess.check_call(cmd)
         except subprocess.CalledProcessError:
-            print('Error running {}'.format(quote_sh_list(cmd)))
+            if self.debug:
+                print('Error running {}'.format(quote_sh_list(cmd)))
             raise
 
     def check_output(self, cmd):
@@ -457,7 +458,8 @@
         try:
             return subprocess.check_output(cmd)
         except subprocess.CalledProcessError:
-            print('Error running {}'.format(quote_sh_list(cmd)))
+            if self.debug:
+                print('Error running {}'.format(quote_sh_list(cmd)))
             raise
 
     def popen_ignore_int(self, cmd):