Remove default=None from config options

In the cfg module default=None is set as the default value.

Change-Id: I5cfc83be010214e2ba8962230766aeb5c5216dc8

manila/share/drivers/emc/driver.py

@@ -50,7 +50,6 @@ EMC_NAS_OPTS = [
                help='Container of share servers.'),
     cfg.StrOpt('emc_nas_pool_names',
                deprecated_name='emc_nas_pool_name',
-               default=None,
                help='EMC pool names.'),
     cfg.StrOpt('emc_nas_root_dir',
                help='The root directory where shares will be located.'),

manila/share/drivers/service_instance.py

@@ -129,7 +129,6 @@ common_opts = [
         help="Password for service instance user."),
     cfg.StrOpt(
         "path_to_private_key",
-        default=None,
         help="Path to host's private key."),
     cfg.IntOpt(
         "max_time_to_build_instance",