Make elasticsearch.in.sh more configurable via env

It's easier to manage a configuration through environment variables than
through a config file if that config file has static values that need to
change each version (such as the ES_CLASSPATH). Trying to keep that in
Chef is tedious whereas just controlling these few settings with
environment variables like most of the other settings in here is simple
and straightforward.
Fixed AOBE when using `top_children` in a must not clause.
Closes #2500
Fixed `top_children` query failure with dfs_query* search types.

Fixed error with the top_children query when `DFS_QUERY_*` is used as search_type and wraps a query that gets rewritten (E.g wildcard query).

Closes #2501
Fix failure message serialization in MultiSearchResponse

Fixes #2498
Added scoring support to `has_child` and `has_parent` queries.

Added score support to `has_child` and `has_parent` queries. Both queries support a score_type option. The has_child support the same options as the top_children query and the none option which is the default and yields the current behaviour. The has_parent query support the score type options: score and none. The latter is the default and yields the current behaviour.

If the score_type is set to a value other than none then the has_parent query map the matched parent score into the related children documents. The has_child query then map the matched children documents into the related parent document. The score_type on both queries defines how the children documents scores are mapped in the parent documents. Both queries are executed in two phases. First phase collects the parent uid values of matching documents with an aggregated score per parent uid value. In the second phase either child or parent typed documents are emitted as hit that have the same parent uid value as found during the first phase. The score computed in the first phase will be used as score.

Closes #2502
Added explain support for nested query.

Closes #2503
Minor changes to the parent / child benchmark.
Upgraded to Lucene version 3.6.2

Closes #2504
Plugins Installer: Allow to download plugins from download.elasticsearch.org
closes #2507.
Allow highlighting on wildcard fields.. ie, comment_*
closes #2396
ShardSearchFailure handling of exception does not take actual into account for status
fixes #2495
match_all filter with empty array (instead of obj) fires exception when used with facets
fixes #2493
optimize filtered query with match_all filter
simply just use the query in that case, and don't add the filter overhead
allow index and type to be specified as arrays in MultiSearchRequest
cleanup
fix type to types
Update settings: Allow to dynamically update thread pool settings

Closes #2509
upgrade to netty 3.6.0
upgrade to jackson 2.1.1
add a sleep to make sure settings are applied