docker-cmd hook handle empty config file

Early in a server boot the file /var/run/heat-config/heat-config may
exist but be empty. This causes a stack trace to be raised in this
script.

This change detects a json parse error and exits gracefully.

Change-Id: I29d731098659bfbf10a2caf80c2cfc49de5df4cc
Closes-Bug: #1648249

hot/software-config/elements/heat-config-docker-cmd/os-refresh-config/configure.d/50-heat-config-docker-cmd

@@ -45,7 +45,7 @@ def main(argv=sys.argv):
     log.setLevel('DEBUG')
 
     if not os.path.exists(CONF_FILE):
-        log.error('No config file %s' % CONF_FILE)
+        log.warning('No config file %s' % CONF_FILE)
         return 1
 
     if not os.path.isdir(WORKING_DIR):
@@ -53,8 +53,9 @@ def main(argv=sys.argv):
 
     try:
         configs = json.load(open(CONF_FILE))
-    except ValueError:
+    except ValueError as e:
-        pass
+        log.warning('Could not load config json: %s' % e)
+        return 1
 
     cmd_configs = list(build_configs(configs))
     try:

tests/software_config/test_hook_docker_cmd.py

@@ -22,7 +22,7 @@ from testtools import matchers
 from tests.software_config import common
 
 
-class HookDockerComposeTest(common.RunScriptTest):
+class HookDockerCmdTest(common.RunScriptTest):
     data = {
         "name": "abcdef001",
         "group": "docker-cmd",
@@ -52,7 +52,7 @@ class HookDockerComposeTest(common.RunScriptTest):
     }
 
     def setUp(self):
-        super(HookDockerComposeTest, self).setUp()
+        super(HookDockerCmdTest, self).setUp()
         self.hook_path = self.relative_path(
             __file__,
             '../..',