move read_blob_file_contents to utils

Thinking ahead, a few other upcoming keystone features could
benefit from reading contents from a file. Thus, moving the
function from policy to utils.

Change-Id: I713ab0e5a00c949ad996daf83b775a7c19044888

openstackclient/common/utils.py

@@ -249,3 +249,13 @@ def get_password(stdin):
             raise exceptions.CommandError("Error reading password.")
     raise exceptions.CommandError("There was a request to be prompted for a"
                                   " password and a terminal was not detected.")
+
+
+def read_blob_file_contents(blob_file):
+    try:
+        with open(blob_file) as file:
+            blob = file.read().strip()
+        return blob
+    except IOError:
+        msg = "Error occurred trying to read from file %s"
+        raise exceptions.CommandError(msg % blob_file)

openstackclient/identity/v3/policy.py

@@ -48,7 +48,7 @@ class CreatePolicy(show.ShowOne):
 
     def take_action(self, parsed_args):
         self.log.debug('take_action(%s)' % parsed_args)
-        blob = _read_blob_file_contents(parsed_args.blob_file)
+        blob = utils.read_blob_file_contents(parsed_args.blob_file)
 
         identity_client = self.app.client_manager.identity
         policy = identity_client.policies.create(
@@ -138,7 +138,7 @@ class SetPolicy(command.Command):
         blob = None
 
         if parsed_args.blob_file:
-            blob = _read_blob_file_contents(parsed_args.blob_file)
+            blob = utils.read_blob_file_contents(parsed_args.blob_file)
 
         kwargs = {}
         if blob:
@@ -174,9 +174,3 @@ class ShowPolicy(show.ShowOne):
                                      parsed_args.policy)
 
         return zip(*sorted(six.iteritems(policy._info)))
-
-
-def _read_blob_file_contents(blob_file):
-    with open(blob_file) as file:
-        blob = file.read().strip()
-    return blob