Shared files in global cache

[adammoody]

This enables one to define a STORE with GROUP=WORLD to use a global file system for cache. Several large issues must be resolved, but this provides enough to run jobs for testing those other work items.

As an example, one can do the following:

First define a WORLD-enabled STORE descriptor. This can be done via an SCR config file or through an SCR_Config API call within the application, e.g.,

SCR_Config("STORE=/p/lustre/$USER/scrcache GROUP=WORLD");

Then at run time, enable cache and point to the STORE location to be used as cache.

export SCR_CACHE_BYPASS=0
export SCR_CACHE_BASE=/p/lustre/$USER/scrcache

A new --global-store option in test_api can be used to specify a directory path. If provided, test_api internally calls SCR_Config to configure that path to be a global store. One can then run test_api and write a shared file to cache. So the full usage looks something like:

export SCR_CACHE_BYPASS=0
export SCR_CACHE_BASE=/p/lustre/$USER/scrcache
srun -n4 -N4 ./test_api --shared-file --global-store $SCR_CACHE_BASE