Output script name and args for debugging purposes

[weshaggard]

Try #2 as the first attempt #481 didn't work in all cases. In particular it doesn't work when you invoke the powershell script across multiple lines as $myInvocation.Line only gives you the first line of context. Why? I have no idea but this new approach seems to work from my limited testing. I guess time will tell if there are any other weird issues.

cc @Azure/azure-sdk-eng

[weshaggard]

As FYI I just found out that this solution will not work either as $args only includes unbound arguments and if a parameter is bound then it will not be shown which is going to be the case for most of our script usages. I've filed an issue with powershell at PowerShell/PowerShell#12609 and once I get more information from that I will update our scripts again with some recommended approach.