[Solstice] migration itests

[wjmelements]

The main actors changing are the miner actor and the reward actor.

SnapDeals probably deserve some itest coverage (see also filecoin-project/builtin-actors#1765).

Some itests may also require updating.

This requires the Solstice builtin-actors changes:

• [Solstice] f02 changes for reward split builtin-actors#1764
• [Solstice] Remove FIL+ and grant all new sectors 10x QAP builtin-actors#1762
• [Solstice] Provide pathway for existing sectors to upgrade to 10x QAP builtin-actors#1763

[rjan90]

@rvagg does filecoin-project/go-state-types#462 also cover the expected migrations itests outlined in this issue?