(PA-5266) Change checksum algorithm to SHA256

Prior to this commit, the puppet_agent::prepare::package class used the
sha256lite algorithm in the file resource for local installation
packages.

In certain circumstances (e.g. when a download is interrupted), this
checksum, which only checks the first N bytes, does not provide
sufficient information to determine if the file is actually there.

This commit updates the file resource to use the more complete sha256
algorithm to handle cases like this.

manifests/prepare/package.pp

@@ -33,6 +33,6 @@
     mode     => $mode,
     source   => $source,
     require  => File[$puppet_agent::params::local_packages_dir],
-    checksum => sha256lite,
+    checksum => sha256,
   }
 }