McLennan: improve logging and diagnostics

[FreddieAkeroyd]

As a developer i would like it to be clearer when there is an issue with the mclennan. This ticket adds various improvements:

• dbior command prints more details
• mclennan change of status (e.g. moving, tracking abort) now printed to log file
• hardware homing does not use SNL for zeroing
• some other default setting from labview now applied on startup
• Also added switch settings and encoder resolution notes to wiki https://github.com/ISISComputingGroup/ibex_developers_manual/wiki/McLennan-motors
• extended emulator and tests
• fixed some use of uninitialised memory and duplicate command issues in driver

acceptance criteria

• Tests run ok
• MacLennan behaviour in office correct, can move and home. I believe this has both a hardware home option and limit switches
• Check ioc log see messages printed about above actions etc about homing, moving. these messages should reflect same status as displayed on crate front panel.
• console to ioc and type dbior and dbior * 1 and check get output, the latter should have the extensive QA command output

[FreddieAkeroyd]

@rerpha have updated ioc/motor/emulator to support HVEL macro and also return output from QA via dbior - see acceptance criteria

[rerpha]

Think I am happy with changes, but still need to test on office mclennan.