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 is necessary as consul-api's tests require a real consul instance
to be running. We can't directly import an agent to fire up an instance,
due to the way this would create an import cycle. These tests instead
will start a consul instance using the binary in $PATH (if it exists).
