6202-1: AFG3021B Make ready for testing

[John-Holt-Tessella]

Before attempting to test in #6202 we need to create a device emmulator, test framework and upgrade the IOC to work with the testing framework.

Acceptance Criteria

• Single dev sim test runs with the AFG3XXX IOC

[John-Holt-Tessella]

PR:

• https://github.com/ISISComputingGroup/IBEX_device_generator/pull/12
• https://github.com/ISISComputingGroup/EPICS-ioc/pull/600
• https://github.com/ISISComputingGroup/EPICS-IOC_Test_Framework/pull/437
• https://github.com/ISISComputingGroup/EPICS-DeviceEmulator/pull/109
• https://github.com/ISISComputingGroup/IBEX/pull/6315

[John-Holt-Tessella]

Added to sprint as sub ticket of 6202

[rerpha]

Have updated https://github.com/ISISComputingGroup/ibex_developers_manual/wiki/Python-versions---2-vs-3 to reflect device generator being updated to py3