automation: avoid '~' in the temp directory on Windows

If a long-ish username is used, the environment variable ends up with a '~' to
be 8.3 path compatible.  That in turn causes a handful of tests (mostly ssh
related) to add quotes around $TESTMP.

I have no AWS experience, so I have no idea if this is the proper way to do it.
But I've hit this problem locally, and redirecting the directory is a
workaround.  I don't recall if the directory is created on demand by the test
harness, but presumably if this is configured before the machine boots, Windows
will do it for us.

Differential Revision: https://phab.mercurial-scm.org/D7130

contrib/automation/hgautomation/aws.py

@@ -191,6 +191,10 b" winrm set winrm/config/client/auth '@{Ba"
 $Setting = 'LocalAccountTokenFilterPolicy'
 Set-ItemProperty -Path $Key -Name $Setting -Value 1 -Force
 
+# Avoid long usernames in the temp directory path because the '~' causes extra quoting in ssh output
+[System.Environment]::SetEnvironmentVariable('TMP', 'C:\Temp', [System.EnvironmentVariableTarget]::User)
+[System.Environment]::SetEnvironmentVariable('TEMP', 'C:\Temp', [System.EnvironmentVariableTarget]::User)
+
 # Configure and restart the WinRM Service; Enable the required firewall exception
 Stop-Service -Name WinRM
 Set-Service -Name WinRM -StartupType Automatic