Refactor tests that use testutil.WaitForResult to use retry.
Since this requires refactoring the test functions in general this patch
also shows the use of the github.com/pascaldekloe/goe/verify library
which provides a good mechanism for comparing nested data structures.
Instead of just converting the tests from testutil.WaitForResult to
retry the tests that performing a nested comparison of data structures
are converted to the verify library at the same time.
This patch stores the datacenter of a node in memdb
and exposes it via the API in all places where a Node
structure is returned.
* /catalog/nodes
* /catalog/node/:node
* /catalog/service/:service
* /health/service/:service
* /query/:uuid/execute
