Update benchmark.asciidoc
Searcher might not be closed if store hande can't be obtained

Today we first get a reference to the IndexSearcher in #acquireSearcher
and then futher down we try to run Store#incRef() which might throw an
exception if the store is already closed. There is a small window
that allows this to happen during InternalEngine#close() when we try
to acquire the searcher at the same time and the engine is the last
resource that holds a reference to the store.

This commit only affects unreleased code since the Store's ref counting
has not yet been released.
Use loopback when localhost is not resolved
we use the "local host" address in sevearl places in our networking layer, if local host is not resolved for some reason, still continue and operate but using the loopback interface
[TEST] make fetch time in millis test more resilient
 beef up the fetch work, and increase teh number of iterations (since we count in nanos, but reports in rounded millis)
Bug fix for hung clients on cluster without benchmark nodes

This is a fix for a bug whereby a cluster that has no nodes started with
-Des.node.bench=true will cause clients to hang if they attempt to
submit a benchmark.

Also adds REST tests to validate fix

Closes #5754