Create global quotas of each type in every NewTestCluster. Also switch some key locks to use DeadlockMutex to make it easier to discover deadlocks in testing.
NewTestCluster also now starts the cluster, and the Start method becomes a no-op. Unless SkipInit is provided, we also wait for a node to become active, eliminating the need for WaitForActiveNode. This was needed because otherwise we can't safely make the quota api call. We can't do it in Start because Start doesn't return an error, and I didn't want to begin storing the testing object T instead TestCluster just so we could call t.Fatal inside Start.
The last change here was to address the problem of how to skip setting up quotas when creating a cluster with a nonstandard handler that might not even implement the quotas endpoint. The challenge is that because we were taking a func pointer to generate the real handler func, we didn't have any way to compare that func pointer to the standard handler-generating func http.Handler without creating a circular dependency between packages vault and http. The solution was to pass a method instead of an anonymous func pointer so that we can do reflection on it.
* Allow max request size to be user-specified
This turned out to be way more impactful than I'd expected because I
felt like the right granularity was per-listener, since an org may want
to treat external clients differently from internal clients. It's pretty
straightforward though.
This also introduces actually using request contexts for values, which
so far we have not done (using our own logical.Request struct instead),
but this allows non-logical methods to still get this benefit.
* Switch to ioutil.ReadAll()
