Ensure we append server_instance to the Errorlog file names so we can distinguish logs from multiple instances

[PiJoCoder]

This is related to the new get_errorlogs.ps1

Do you want to request a feature or report a bug?
Likely a bug

What is the current behavior?
Need to test with multiple instance of the same version - not sure

*If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem **
Install 2 SQL instances of the same version
Run PSSDIAG using SQL Base collector (on by default) and check the ERRORLOG files

What is the expected behavior?
To have ERRORLOGs collected from all instances under investigation

Possible solution
Rename the files by appending the servername_instance to the file as we are copying them

[PiJoCoder]

FYI @Peter-Msft . We hadn't considered the scenario of multiple instance of the same version. This would take care of it.