{Core} Only lower provisioning_state when it has value

[jiasli]

Fix the regression in #12154: provisioning_state.casefold() raises exception AttributeError: 'NoneType' object has no attribute 'casefold' when provisioning_state is None.

This causes issue to az sql server wait since sql server doesn't use "provisioningState": "Succeeded", but "state": "Ready": #12313

Only lower provisioning_state when it has value (not None or empty string '').

Tested with

az vm wait --ids {} --created

Also, use lower() to be consistent with other code.

[fengzhou-msft]

LGTM, thanks for the fix.

[Juliehzl]

My concern is that although your current change will not break users ay more, the sql wait command still doesn't work now.
I mean because the wait condition is from "state" and "provisionstate" will none, the wait condition will never match as expected for this scenario.

[jiasli]

My concern is that although your current change will not break users ay more, the sql wait command still doesn't work now.
I mean because the wait condition is from "state" and "provisionstate" will none, the wait condition will never match as expected for this scenario.

I have put my thought in #12313 (comment). But anyway, let's fix the regression first.