Bug fixes for Ares

[ChristopherHogan]

• Hermes cores need RPC clients. Previously just the application cores had them.
• Converted several RPCs that returned void to return a bool. We don't actually use the result, but it has the effect of making the call synchronous. Previously, when the calls were asynchronous (meaning the caller didn't have to wait for a response), we had an eventual consistency model, so it was possible for a Get to not see metadata that an immediately preceding Put updated. We may switch back to eventual consistency at some point for performance reasons, but right now I prefer deterministic correctness.

[coveralls]

Pull Request Test Coverage Report for Build 537712821

• 20 of 54 (37.04%) changed or added relevant lines in 5 files are covered.
• 16 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.2%) to 80.216%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/buffer_pool.cc	1	6	16.67%
src/metadata_management.cc	0	14	0.0%
src/rpc_thallium.cc	16	31	51.61%

Files with Coverage Reduction	New Missed Lines	%
src/buffer_pool.cc	1	78.28%
src/rpc_thallium.cc	15	61.71%

Totals
Change from base Build 522452615:	-0.2%
Covered Lines:	4225
Relevant Lines:	5267

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💛 - Coveralls

[jya-kmu]

If it can simplify something at this point it is fine. Yet we may create a bookmark for this change since we expect performance issue in the future especially when scaling.