Don't fail if an output filter doesn't have groups

Previously, any output filter patterns needed to have at least one group
indicated by a set of parentheses. This didn't take into account the use
case where the user doesn't care about capturing output, only wants to
verify that certain output existed. This fixes that shortcoming.

Author: mmabey

vagrant/__init__.py

@@ -1015,15 +1015,19 @@ def _filter_vagrant_command(self, args, output_filter):
 
             # Parse command output for the specified filters. Method used depends on version of Python.
             # See http://stackoverflow.com/questions/2715847/python-read-streaming-input-from-subprocess-communicate#17698359
-            if not py3:  # Python < 3.0
+            if not py3:  # Python 2.x
                 p = subprocess.Popen(**sp_args)
                 with p.stdout:
                     for line in iter(p.stdout.readline, b''):
                         pop_key = None
                         for f in output_filter.keys():
                             m = re.search(output_filter[f]['pat'], line)
                             if m:
-                                filter_results[f] = m.group(output_filter[f]['group'])
+                                try:
+                                    filter_results[f] = m.group(output_filter[f]['group'])
+                                except IndexError:
+                                    # User must have not included parenthases in their pattern
+                                    pass
                                 # No need to search for this pattern again in future lines
                                 pop_key = f
                                 break
@@ -1038,7 +1042,11 @@ def _filter_vagrant_command(self, args, output_filter):
                         for f in output_filter.keys():
                             m = re.search(output_filter[f]['pat'], line)
                             if m:
-                                filter_results[f] = m.group(output_filter[f]['group'])
+                                try:
+                                    filter_results[f] = m.group(output_filter[f]['group'])
+                                except IndexError:
+                                    # User must have not included parenthases in their pattern
+                                    pass
                                 # No need to search for this pattern again in future lines
                                 pop_key = f
                                 break