[BYOC][ACL] Enable remote device via environment variables (#6279)

[BYOC][ACL] Enable remote device via environment variables (#6279)

* [BYOC][ACL] Enable remote device via environment variables

Improves the ACL remote testing infrastructure by allowing a remote device to be specified via environment variables. This means external scripts can be used to enable the runtime tests. By default an RPC server will not be used and the runtime tests will be skipped.

Change-Id: I8fc0b88106683ac6f1cbff44c8954726325cda21

* Use json file as configuration for tests

Change-Id: Iadce931d91056ed3a2d57a49f14af1ce771ae14b

* Do not load the test config during class creation

Change-Id: If718b5d163e399711111830f878db325db9c5f84

* Add check for existence of file

Change-Id: I2568bca7f4c3ad22ee8f9d065a9486ee3114f35c