Remove broken reservation_test.py and refactor acquire and reserve managers

The bazel.labgrid.client.reservation_test.py no longer works as it was written to use the lock.py and reserve.py that sits alongside it and they were originally created for the crossbar Labgrid solution.

Recently as part of !129 and !135 we've added replacement versions of this functionality which works for the new gRPC Coordinator solution.

Due to this we should remove these portions of code that no longer work, this includes:

bazel.labgrid.client.reserve.py
bazel.labgrid.client.lock.py
bazel.labgrid.client.reservation_test.py

Once that's done we should look at possibly refactoring out the reserve and acquire managers from bazel.labgrid.manager, and have the core functionality be in bazel.labgrid.client like the previous reserve.py and lock.py were.

The bazel.labgrid.manager portion of the code will just reference the core functionality from bazel.labgrid.client and wrap it in the Manager related code.

This additional refactoring has come from: https://gitlab.arm.com/bazel/rules_labgrid/-/merge_requests/135#note_158658