1. The individual test files (.ps1) in `/test/powershell/engine` are moved to the corresponding subfolders.
2. The test asset file `test/powershell/Common/TestTypeFile.ps1xml` is moved to `test/powershell/Common/engine/Api/assets/` so that it's next to the test that is using the file.
* corrected use of PSModulePath casing to be consistent with Windows PowerShell
addresses #3227
* addressing review feedback
make "PSModulePath" into const
fixed some test workarounds due to failures for external reasons that wasn't meant to be checked in
* addressing review feedback
make "PSModulePath" into const
fixed some test workarounds due to failures for external reasons that wasn't meant to be checked in