[Miner] Miner should extend its tenure even if it didn't produce the stacks tip when there is an unresponsive sortition winner

[jferrant]

Currently we do not handle the following tenure extend case:

Miner A wins tenure A.
Miner B wins tenure B BEFORE Miner A manages to issue a BlockFound.
Miner B fails to produce a block by Miner A's tenure_extend_wait_timeout
Miner A SHOULD issue a late block found then a tenure extend for tenure A.

Similarly, Miner A wins tenure A.
Flashblocks occur
Miner B wins tenure B BEFORE Miner A manages to issue its late BlockFound.
Miner B fails to produce a block by Miner A's tenure_extend_wait_timeout.
Miner A SHOULD issuea. late block found then a tenure extend for tenure A.

As the code is set up now, Miner A will only consider extending its tenure during a sortition with a winnner if it won the ongoing tenure sortition (i.e. it produced the last stacks block). In the two above scenarios, it has not (since it never produced a block) and therefore just stop its tenure without attempting a delayed tenure start/extend. Fix this and add the above two testing scenarios.