SQL VM Powershell cmdlets

SQL IaaS Powershell cmdlets
Scenarios:
1) Gets current SQL IaaS’s guest agent extensions configuration 
2) Sets SQL IaaS’s guest agent extensions configuration 
     - Enable/ Disable / Configure Auto-patching settings
     - Enable/ Disable / Configure Auto-backup settings
3) Removes SQL IaaS’s guest agent extension. 

Test cases:
- Added functional tests for SqlIaaSAgent extension