CA-122801] If there is no NSIS, But WMI works, update NSIS before continuing

Also, rename NSISuninstalling to NSISHandlingRequired to avoid confusion (as
this is used both when NSIS needs to be installed and when it needs to be
uninstalled)

Signed-off-by: Ben Chalmers <Ben.Chalmers@citrix.com>
Merge pull request #26 from benchalmers/ca-122801

CA-122801] If there is no NSIS, But WMI works, update NSIS before contin...