(PUP-390) arch is more correct terminology over platform

Prefer the use of architecture over platform as it is more consistent with
other operating systems and reduces confusion on the terminology.
(PUP-390) Append -x64 to msi name

 - When the architecture is x64, append that to the name.  e.g. puppet.msi
becomes puppet-x64.msi when ARCH=x64.
- Allow a file name to be passed to the script as PKG_FILE_NAME so the signtool
cant be passed the name of the particular package for signing.
- Passing PKG_FILE_NAME to windows:build will use the name passed in as the
name of the MSI. e.g. PKG_FILE_NAME=puppet.3.6.2-x64.msi will result in a file
named puppet.3.6.2-x64.msi in the pkg folder.
 - Allow install/uninstall to use PKG_FILE_NAME to perform install/uninstall
based on name of package passed in.