[TEST] Stabelize test - wait for yellow to ensure all primaries are allocated
Better default size for global index -> alias map
The alias -> (index -> alias) map, specifically the index -> alias one, typically just hold one entry, yet we eagerly initialize it to the number of indices. When there are many indices, each with many aliases, this is a very large overhead per alias...
closes #6504
[DOCS] Fixd typo in http.asciidoc
[TEST] consistently omit norms in test otherwise scoring will be dependent on merges etc.
[TEST] Force flush even if not needed to ensure successful shards is greater than 0
[TEST] Add basic Backwards Compatibility Tests

This commit add a basic infrastructure as well as primitive tests
to ensure version backwards compatibility between the current
development trunk and an arbitrary previous version. The compatibility
tests are simple unit tests derived from a base class that starts
and manages nodes from a provided elasticsearch release package.

Use the following commandline executes all backwards compatiblity tests
in isolation:

```
mvn test -Dtests.bwc=true -Dtests.bwc.version=1.2.1 -Dtests.class=org.elasticsearch.bwcompat.*
```

These tests run basic checks like rolling upgrades and
routing/searching/get etc. against the specified version. The version
must be present in the `./backwards` folder as
`./backwards/elasticsearch-x.y.z`
[TEST] Add test for accessing _score in scripts
[TEST] Fix test cluster naming

This commit renames `TestCluster` -> `InternalTestCluster` and
`ImmutableTestCluster` to `TestCluster` for consistency. This also
makes `ExternalTestCluster` and `InternalTestCluster` consistent
with respect to their execution environment.

Closes #6510
[DOCS] Fixed is/if typo in Api Conventions doc
[TEST] wait for ongoing recoveries to finish. Flush fails on shards otherwise.