add test for ElasticSearchPostingsFormat
[TEST] use assertAcked when creating indices
ignore index if it's not in the cluster state and it's in the drop indices set

Closes #5643
[TEST] Expect all shards to fail if full refresh failed
Throw EngineClosedException if engine is closed

Currently we throw misleading exception in acquireSearcher
if we try to acquire while we are failing the engine. We should
throw an EngineClosedException instead.

Relates to #5633
Enrich exception message if searcher can not be aquired

This commit also moves the log message after the ensureOpen() call
to only log an error if it's really an erro condition.
[TEST] Add ThreadLeaks protection to ElasticsearchPostingsFormatTest since we keep running clusters around in the JVM
[TEST] Removed last occurences of cluster_seed, no longer used

Relates to #5233
[TEST] Add ability to start nodes in async mode in TestCluster
this will help speed up when starting multiple nodes in a test
closes #5644
[TEST] Print out the `tests.cluster` sys prop if available to be able to reproduce failures when using the external cluster

Relates to #5630
[TEST] fixed typo in ReproduceInfoPrinter (s/nighly/nightly)
Geo: Allow to parse lat/lon as strings and coerce them

In order to be more failsafe parsing GeoPoints can support
lat/lon as strings and coerce them. Added support and test for this.
[TEST] use length-norm as the tie-breaker in BlendedTermQueryTest
[DOC] Fixed flags example incorrect syntax
Upgrade to Lucene 4.7.1

 * Removed XTermsFilter fixed in LUCENE-5502
 * Switched back to automaton queries that caused failures due to LUCENE-5532
 * Fixed Highlight test that has different results due to LUCENE-5538
Added an indices level field data cache listener that always gets invoked and updates indices statistics and services about field data loading and unloading.

Moved the circuit breaker memory reducing logic to the IndicesFieldDataCacheListener, so it always reduces the memory used when field data gets unloaded,
this fixes a issue where the circuit breaker didn't get reduced when segments where no shardId could be resolved get cleared up.

Also made sure that exceptions in the percolator service are bubbled up properly.

Closes #5588
Removed incorrect comment
[Tests] Reduce the number of threads used by the BackgroundIndexer by default

It sometimes overloads the nodes.
Typo in the description for include_in_all

I know this is uber-minor, but I was confused by the phrase "the raw field value to be copied". I assume "is" was supposed to be instead of "to"
Freq Terms Enum
A frequency caching terms enum, that also allows to be configured with an optional filter. To be used by both significant terms and phrase suggester.
This change extracts the frequency caching into the same code, and allow in the future to add a filter to control/customize the background frequencies
Closes #5597