Updated the description for StayProvisioned parameter per Bug931236

[sdwheeler]

Description

From https://mseng.visualstudio.com/TechnicalContent/_workitems/edit/931236

It appears for all versions of the AzureRM.Compute module, the description of the parameter -StayProvisioned is incorrect and raised by CSS during the Automation bug bash call today.  The description is incorrect because that switch is to prevent deallocation. 

The description should say something like "Indicates that this cmdlet stops all the virtual machines within the VMSS and does not deallocate them.  The user is charged for the stopped virtual machines."

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