Description
===========
The dell_nas_backend_port has a default value of 443. However, if this parameter is not defined in the configuration, it should default to this value, but instead, it results in errors.

Steps to reproduce
==================
1. Remove the configuration parameter key dell_nas_backend_port from manila.conf file

Expected result
===============
The manila share service should start with the default port value which is 443.

Actual result
=============
Getting errors
May 17 05:29:30 host001010 manila-share[101219]: ERROR manila.share.manager self.plugin.connect(self, context)
May 17 05:29:30 host001010 manila-share[101219]: ERROR manila.share.manager File "/opt/stack/manila/manila/share/drivers/dell_emc/plugins/powerflex/connection.py", line 103, in connect
May 17 05:29:30 host001010 manila-share[101219]: ERROR manila.share.manager self.rest_port = (int(get_config_value("dell_nas_backend_port")) or
May 17 05:29:30 host001010 manila-share[101219]: ERROR manila.share.manager TypeError: int() argument must be a string, a bytes-like object or a real number, not 'NoneType'