mining: return witness_script instead of raw witness_commitment in GBT

[roylee17]

The "default_witness_commit" in the getblocktemplate response uses the witness_script instead of raw commitment.

[coveralls]

Pull Request Test Coverage Report for Build 1850844731

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 79.676%

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Totals
Change from base Build 1808348675:	0.0%
Covered Lines:	1231
Relevant Lines:	1545

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💛 - Coveralls

[roylee17]

@Roasbeef

[Roasbeef]

@roylee17 slipped by initial due to a lack of integration tests in this area. Would you mind adding a new test in the integration folder? It would use GBT to construct a new block and then assert that we also accept that same block.

[roylee17]

[Accidentally deleted the branch, which generates the, PR.]

@Roasbeef I'll look into how to create that test.