[util/cli] Add option to ignore return codes

Add an option that ignores the return code of an execute, instead of
throwing an error (which sometimes causes ugly try/except blocks in
client code)

tests/util/test_cli.py

@@ -26,6 +26,12 @@ class cli(unittest.TestCase):
         with self.assertRaises(RuntimeError):
             util.cli.execute('cat {}'.format(self.nonExistentCommand))
 
+    def test_command_exit_code_no_error(self):
+        try:
+            util.cli.execute('cat {}'.format(self.nonExistentCommand), ignore_errors=True)
+        except Exception:
+            self.fail('exception was thrown')
+
     def test_async(self):
         rv = util.cli.execute(self.validCommand, wait=False)
         self.assertEqual('', rv)

util/cli.py

@@ -2,7 +2,7 @@ import shlex
 import subprocess
 import logging
 
-def execute(cmd, wait=True):
+def execute(cmd, wait=True, ignore_errors=False):
     args = shlex.split(cmd)
     logging.debug(cmd)
     try:
@@ -12,7 +12,7 @@ def execute(cmd, wait=True):
 
     if wait:
         out, _ = proc.communicate()
-        if proc.returncode != 0:
+        if proc.returncode != 0 and not ignore_errors:
             raise RuntimeError('{} exited with {}'.format(cmd, proc.returncode))
         return out.decode('utf-8')
     return ''