Move AdjustableRoundsManager from protocol directory to contract tests directory

[RiccardoBiosas]

What does this pull request do? Explain your changes. (required) It moves the AdjustableRoundsManager contract from the protocol /rounds directory to the tests /mocks directory as it is a contract that is meant to be used only for testing.

Specific updates (required) contracts/rounds/AdjustableRoundsManager.sol -> contracts/test/mocks/AdjustableRoundsManager.sol

How did you test each of these updates (required) Successfully run the protocol's test suite.

Does this pull request close any open issues? No

Checklist:

• [ ] README and other documentation updated
• [x] All tests using yarn test pass

[coveralls]

Pull Request Test Coverage Report for Build 2548913771

• 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 99.372%

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Totals
Change from base Build 2548785832:	0.0%
Covered Lines:	778
Relevant Lines:	781

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💛 - Coveralls