assign variables to build object in 10_setupvars.rake

This commit updates 10_setupvars.rake to create a BuildInstance object and
assign our various settings to it, rather than global instance variables. We
defeated encapsulation at the origin of the packaging repo, but here it makes a
defiant return. This commit also modifies variable loading to load everything
from a yaml file we pass in the path to with the PARAMS_FILE environment
variable. This takes advantage of the BuildInstance ability to read in
attributes from a yaml file and write them back out again. We also don't need
explicit parameter setting any more for the most part, since the build object
will read in for us, but we keep the ability to override some parameters with
environment variables.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>
1 to 1 mapping in params and variable names

Why I ever decided to name the instance variables something other than
their respective yaml file entries is beyond me. This commit starts on
some of the work of fixing this, by replacing all instances of @name
with @project, which is what it is in the project_data.yaml file.