Implement LAVA jobs for microinstance - TCWG-432 [6/10]
* Refactoring to permit sharing of code between uinstance & main
instance, as far as possible
* Further refactoring for sane submission of bundles without inserting
LAVA assumptions in the wrong places
* Tested as far as possible in main insta
* Off on Wed afternoon [1/10].
# Progress #
* Fails in gdb.threads/multiple-step-overs.exp, (TCWG-332) [1/10]
Patch V2 is posted, pending for review.
* TCWG-422, patch is committed. Done. [2/10].
* TCWG-423, patches are ready, being regression tested. [2/10]
* TCWG-433, build GDB with -fsan
