[minor] Improving cluster management

[YgorCastor]

• Added healthcheck to each node, now if a node is unreachable the driver will remove it from the pool.
• Added round-robin to select nodes.

[coveralls]

Pull Request Test Coverage Report for Build 3741a693932ece654bb77f68effb289cca16305c-PR-17

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 42 of 50 (84.0%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.3%) to 86.028%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
lib/connection/models/node_selector.ex	12	13	92.31%
lib/connection/executor/request_executor.ex	9	12	75.0%
lib/connection/executor/supervisor.ex	16	20	80.0%

Totals
Change from base Build a226dfdafd1153d5e3dc3cf3612af87732fc953d:	-0.3%
Covered Lines:	665
Relevant Lines:	773

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💛 - Coveralls