Optimize "open" method with context manager

Use opening context manager to open a file.

Change-Id: I07ea2f163b101e9501ee54b1f5de924895b35e64

heat/cloudinit/loguserdata.py

@@ -116,8 +116,5 @@ if __name__ == '__main__':
 
     provision_log = os.path.join(VAR_PATH, 'provision-finished')
     # touch the file so it is timestamped with when finished
-    pl = open(provision_log, 'a')
-    try:
+    with open(provision_log, 'a'):
         os.utime(provision_log, None)
-    finally:
-        pl.close()

heat/cloudinit/part_handler.py

@@ -35,23 +35,14 @@ def handle_part(data, ctype, filename, payload):
     if ctype == "__end__":
         return
 
-    log = open('/var/log/part-handler.log', 'a')
-    try:
-        timestamp = datetime.datetime.now()
+    timestamp = datetime.datetime.now()
+    with open('/var/log/part-handler.log', 'a') as log:
         log.write('%s filename:%s, ctype:%s\n' % (timestamp, filename, ctype))
-    finally:
-        log.close()
 
     if ctype == 'text/x-cfninitdata':
-        f = open('/var/lib/heat-cfntools/%s' % filename, 'w')
-        try:
+        with open('/var/lib/heat-cfntools/%s' % filename, 'w') as f:
             f.write(payload)
-        finally:
-            f.close()
 
         # TODO(sdake) hopefully temporary until users move to heat-cfntools-1.3
-        f = open('/var/lib/cloud/data/%s' % filename, 'w')
-        try:
+        with open('/var/lib/cloud/data/%s' % filename, 'w') as f:
             f.write(payload)
-        finally:
-            f.close()

heat/tests/test_template_format.py

@@ -71,11 +71,12 @@ class JsonToYamlTest(common.HeatTestCase):
         for path in os.listdir(dirpath):
             if not path.endswith('.template') and not path.endswith('.json'):
                 continue
-            f = open(os.path.join(dirpath, path), 'r')
-            json_str = f.read()
+            with open(os.path.join(dirpath, path), 'r') as f:
+                json_str = f.read()
+                f_name = f.name
 
             yml_str = template_format.convert_json_to_yaml(json_str)
-            yield (json_str, yml_str, f.name)
+            yield (json_str, yml_str, f_name)
 
     def test_integer_only_keys_get_translated_correctly(self):
         path = os.path.join(os.path.dirname(os.path.realpath(__file__)),