Add EPICS unit and integration tests

[ralphlange]

pvsSrv should contain unit tests (in the EPICS Base sense) that can be automatically run during build.
These tests should not only test advertised features, but also error returns, bad data, drive limits, etc.

The location should be testTop for integration tests, i.e. stuff with separate server and client processes.
Unit tests, i.e. single process tests, should be part of the main structure, as they are expected to be run as part of the regular build.