* Set the "build_jobs" on concretization/generate for CI
build_jobs also controls the concretization pool size. Set this
in the config section for CI generate.
This config is overwritten by build_job CI using the SPACK_BUILD_JOBS
environment variable. This implicitly will drop the default build
CPU request on all "default" grouped build jobs from (max) 16 to 8.
* Add default allocations for build jobs
* Add common jobs and concretize args to ci generate and rebuild
* CI: Specify parallel concretize and build jobs via argument
* Increase power and cray concretization limits
Lowering limits for these stacks creates timeout
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