Enforce java version 1.7

When building elasticsearch, we now require to use java 1.7.

Maven will check that before compiling any class. If Java version is incorrect, you will get the following message:

```
[WARNING] Rule 0: org.apache.maven.plugins.enforcer.RequireJavaVersion failed with message:
Detected JDK Version: 1.6.0-65 is not in the allowed range [1.7,).
```

Closes #5428.
[Test] IndexLifecycleActionTests - set minimum master node earlier to make sure it's in effect when needed.
[Test] FullRollingRestartTests - correctly setting minimum_master_nodes

Also added a ElasticsearchIntegrationTest.setMinimumMasterNodes() helper function.
[Tests] QuorumLocalGatewayTests - Set mini_master_nodes earlier to make sure it has effect.  ClusterServiceTests - remove a thread.sleep in favor of awaitBusy
[Docs] added a missing reference to significantterms-aggergations

Also fix header level mismatch issue reported by the build
[DOCS] Updating scripting docs for geo functions

Added a few functions are corrected the default unit where necessary
[DOCS] Fix typo in the reference doc. SuSe -> SUSE

SUSE, as a Linux distribution, is never lower cased

fixes #5354
[DOCS] Reword clear-scroll sentence
[DOCS] Fixing contributing.md indentation

Add a whitespace to make these separate paragraphs inside of a list.