2018-11-30: FG; Touch gnocchi-api.log file.

lib/charm/openstack/gnocchi.py

@@ -70,6 +70,8 @@ def log_config(config):
     gru = GnocchiCharm.group
     uid = pwd.getpwnam(usr).pw_uid
     gid = grp.getgrnam(gru).gr_gid
+    # touch file
+    open(log_config_file, 'a').close()
     os.chown(log_config_file, uid, gid)
     return log_config_file