2853: Use rendezvous hashing to select probe order.
2853: Use rendezvous hashing to select probe order in Python library.
2853: Fix instance ID in test fixture hostnames. Clean up brittle tests.
2853: Add "reference set" test to check probe order agreement between implementations.
2853: Add tests for reference set and some edge cases.
2853: Update tests to survive ServiceRoots being a map[string]string.
2853: Use the same keep_service UUIDs so tests behave reliably.
2853: Add comment.
2853: Remove shuffledServiceRoots() wrapper.
2853: Merge branch 'master' into 2853-rendezvous

Conflicts:
	sdk/python/arvados/keep.py
2853: Remove redundant test case.
2853: Use Md5String() in getWeight().
2853: Fix reference to reference set.
2853: Avoid using reserved word "hash" as a variable name.
2853: Use mock from KeepClientServiceTestCase for rendezvous tests
instead of intruding on KeepClient's private instance variables.
2853: Merge branch 'master' into 2853-rendezvous
Merge branch '2853-rendezvous' closes #2853