Set nowInMillis to search context created by the count api so that "NOW" can be used within queries

Added nowInMillis to ShardCountRequest in a backwards compatible manner

Fixes #3625
Set nowInMillis to search context created by the validate query api so that "NOW" can be used within queries

Added nowInMillis to ShardValidateQueryRequest in a backwards compatible manner

Fixes #3629
Set nowInMillis to search context created by the explain api so that "NOW" can be used within queries

Added nowInMillis to ExplainRequest in a backwards compatible manner

Fixes #3626
Added the clear_scroll spec
don't clear gateways in reroute test
- also remove test logging from percolator
Moved SimpleIndexStateTests to AbstractIntegrationTest
Add/fix index selectors.

Closes #3758.
More AbstractIntegrationTest
Added @TestLogging to all methods to see which shards we refresh and which ones we search on

Increased wait timeout and added multiple iterations there as well, one is not enough. We want to verify whether the problem gets fixed later on.
fix log to trace
Fixed serialisation bug for multi percolate request and response classes.

This bug manifests when running with transport client.
Add listener nodes to nodes list if 'sniff' is true

TransportClient doesn't add the initial nodes to the nodes list
if it doesn't retrieve any nodes from the listeners which can cause
the transport client to throw a 'NoNodeAvailableException' if the
'sniff' response didn't return any nodes. This situation can occure
if the client tries to get the listener nodes cluster state while that
node is not yet connected to any other nodes.
Fail GetIndexTemplate if names it null or empty
Call validate in TransportClients before request is send
Add missing TransportHandler for clear_sc (ClearScroll)
Small cleanups in TransportClient et.al

Catching Throwable instead of Exception in TransportClient
and TransportClientNodesService and restore interrupted flag
if interrupt exception is caught and ignored
Cleanup Integration Tests
Add completion field support in Rest nodes stats

Closes #3746
add internal source to refresh
can be used to more easily understand where its coming from
add internal source to acquire searcher
add a source indicating why the searcher was acquired