Fix ordering problem in loading of variables

This commit updates the ordering of loading data into Pkg::Config. The prescribed order is:

1) Load default values we establish in the packaging repo

2) Load values set withing the project_data.yaml and build_defaults.yaml files

3) Load versioning data obtained via `git`

4) Load override data obtained via ENV['PARAMS_FILE']

5) Load data obtained via environment varialbes

6) Load data obtained by assigning old variable values to their new counterparts

This order reflects precedence via ordering - the things loaded last override
the things loaded first.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>