Consider using more variables in template files

[jodh-intel]

Each template file has a few fields that are repeated and which could be replaced by a variable (as done for things like @GO_VERSION@).

For example, the following is common to most of the rpm template files:

%global DOMAIN github.com
%global ORG clearcontainers

.. and again, most spec file templates contain things like:

%global PROJECT proxy
Name: cc-proxy

... which could be generated from the corresponding update_proxy.sh (or other update_*.sh script [*]).

This sort of refactoring is going to make maintaining these packages easier, ensures the metadata is consistent and would make it easy to rename the packages should we need to in the future.

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[*] - It may even be possible to refactor all the update_*.sh scripts further so that more is pushed into ./scripts/pkglib.sh.