[Debugging] fix test "testMineAttempt"

[bbulgu]

org.opentest4j.AssertionFailedError: new block was not properly added ==> Expected :11001110000100100000100111010135706429811001110000100100000100111010123355960oayxbzqjbd Actual :000000000000000000000000000000357064298

Suggestion: investigate whether the flag is updated correctly, i.e., after mining a new block the flag should point to it: blk.numID = flag.nameID

In general always flag.nameID should point to the latest block, and flag.numID should always be zero.

Please add a test verifying that when a block is mined correctly we have the flag updated accordingly.