testsuite: Refactor withShorterPathForNewBuildStore
This makes `withShorterPathForNewBuildStore` fit more nicely into the
rest of the testing infrastructure.
* Move `withShorterPathForNewBuildStore` to `TestM` monad
* Move responsibility for passing `--store-dir` to `cabalGArgs` function
* Move `findDependencyInStore` into `TestM`, and remove requirement to
pass path to store directory.
* Introduce `testStoreDir` function which returns the store location
(and honours `withShorterPathForNewBuildStore`)
* Migrate tests which use `withShorterPathForNewBuildStore`.
23 files changed: