Fixed an issue where there are sug aggregations executing on a single shard, the reduce call was not propagated properly down the agg hierarchy.

Closes #4843
fixed license header indentation
[DOCS] More assertive statement about requiring `query` in _count, etc
Serving _site plugins do not pick up on index.html for sub directories

If one asks for `http://es:9200/_plugin/PLUGIN_NAME/` and the the plugin's _site directory contains an index.html file, it will be correctly served.

This is not the case for sub directories: a _site/folder/index.html is not served when requesting  `http://es:9200/_plugin/PLUGIN_NAME/folder/` but one gets a 403 Forbidden response as if trying to browse the folder.

Closes #4845.
fixed the reduce of InternalGeoHashGrid when executing on a single shard
Added more unit like test that verifies that has_child is never cached even if wrapped by another filter.
Throw exception if `cluster.name` is specified in TestCluster node settings

We rely on the `cluster.name` setting to be the same across all nodes
and transport clients etc. If a node setting contains `cluster.name`
the test might not work if a random transport client is swapped
in. Passing such a configuration should result in an exception since
it's clearly an illegal state.
Use different field names based on the data type in aggregations tests.

Tests fail once in a while because of a ClassCastException at the mvel level.
We suspect that this happens because a script that is JIT-ed on a specific
data type cannot later be used with another one, but we didn't manage to
reproduce in our development environments, so let's try to change the field
names to see if this error keeps occurring.
Re-Sort config/names
Removed old serialization logic (<= 1.0-RC1) in readFrom and writeTo methods.
Removed duplicated registration of warmers as custom metadata type

Already done in a static block within IndexMetaData
Removed put/delete warmer tests that were meant to test that the serialization was bw compatible after adding support for acks
Removed redundant version checks in transport serialization (#4731 leftover)
Remove duplicate cache columns
Normalize cat headers, add aliases

Closes #4852.
Add tera and peta to RestTable.renderValue()

Closes #4871
Install SecurityManager inside ElasticsearchTestCase for easier randomization

We currently run always with SecurityManager installed. To make sure we
work also without we should randomly swap it out ie. run without the
security manager.