Correct package:<version> tasks (for backward compatibility)

When the build system data moved under Pkg::Config, it was no longer accessible
as instance variables of the Rake invocation, thank heavens. However, this
broke references to `self` attempting to access this data, including these rake
package:<version> tasks. This commit updates them. Note, however, that these
are DEPRECATED in favor of doing `rake pl:print_build_param[:param]` which give
access to *all* Pkg::Config data, not just these select few. However, since to
print a warning would be backwards incompatible, we're kind of stuck with these
for now.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>