Expose a full read-only view of System to user checks #70
Description
Currently, the system-level directories are writeable, because the CLI must be able to set them. As a result, a user check may also set them. This does not affect the rest of the checks, since each check runs isolated. However, we want to disallow this. We can achieve this by creating an adapter layer above System that will expose a read-only view to the RegressionTest.
Internal issue: https://madra.cscs.ch/scs/reframe/issues/393