Use os.getlogin() to set the User for the discovery service job

[civerachb-cpr]

Description

Replace User=ubuntu with User={os.getlogin()} when generating the discovery server configuration file if necessary

Fixes #14

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Simple text replacement; unit test of new function only.

Did not generate a non-standard Ubuntu installation & run the whole script.

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation