Check_drivesize : Non-empty drives return OK state instead of UNKNOWN

[inqrphl]

• add error types to the helper functions of check_drivesize
• use error types and typecasting to see if no drives are found
• return OK state if no drives are found
• write non-existent drive tests for check_drivesize
• also test customizing empty state result using empty-state= argument

[inqrphl]

I only tested it on Linux. Is this behavior expected from Windows as well?

This checks Implemented field is set to ALL. On windows it uses the definitions made in check_drivesize_windows.go file. I can also add these error types to Windows helper functions as well.

[sni]

Is this behavior expected from Windows as well?

Yes please, this check should behave the same way across all supported platforms.