test_services.py flaky test.

[fchirica]

Fixes the flakiness of test_services.py: the function find_available_listen_port would rarely give an already in use port. This PR enhances the logic of find_available_listen_port. During the stress testing, it no longer returned already in use ports. Additionally, it fixes a (theoretical) race where tests would run in parallel and find_available_listen_port would give the same port by setting parallel=False.

[coveralls-official]

Pull Request Test Coverage Report for Build 6431831714

• 8 of 9 (88.89%) changed or added relevant lines in 2 files are covered.
• 70513 unchanged lines in 571 files lost coverage.
• Overall coverage decreased (-73.4%) to 16.162%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
chia/simulator/socket.py	7	8	87.5%

Files with Coverage Reduction	New Missed Lines	%
chia/consensus/constants.py	1	92.65%
chia/consensus/pos_quality.py	1	80.0%
chia/full_node/fee_estimation.py	1	97.62%
chia/protocols/pool_protocol.py	1	98.46%
chia/server/outbound_message.py	1	95.83%
chia/types/blockchain_format/reward_chain_block.py	1	97.56%
chia/util/db_synchronous.py	1	75.0%
chia/util/permissions.py	1	88.89%
chia/wallet/uncurried_puzzle.py	1	90.0%
chia/wallet/util/notifications.py	1	87.5%

Totals
Change from base Build 6425197397:	-73.4%
Covered Lines:	17030
Relevant Lines:	97723

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💛 - Coveralls