Fixed case where comparing stdout bytes to a string issue 797

[jineshcodes]

Incident ID or link	#797
Issue summary	Configurations with nxService resource where the service falls under servicemd fails for Python3 during get_marshall()
Impact	All distros running on python 3 will not be able to use configurations which try to set service that falls under servicemd for nxService resource. The service will not crash but fail gracefully.
Root cause	The reason the get_mashall() is failing is because of a comparison  between string and stdout. For python 3 stdout can be in bytes. Issue in line: https://github.com/microsoft/PowerShell-DSC-for-Linux/blob/v1.2.0-0/Providers/Scripts/3.x/Scripts/nxService.py#L858
Reason for not getting caught before release	This scenario was not covered as a part of test suite or manual tests. Manual tests were only done for major scenarios and not for corner cases.