Unique cloud name per launch
Fix API documentation.
Upgrade dependencies.
WIP: Simple cache for RDDs.
Sparkling Water infrastructure refactored.
Enabling scalatests in gradle files.

Creating proper environment for test:
 - for local[*] only launch classes are required
 - for local-cluster[*] test assembly is provided
   - assembly contains: core, h2o-core, h2o-app, joda, ... libraries
Output of test is put into build/unit-tests.log
Sharing scalatest setup croess scala projects.
Upgrading gradle wrapper.
Comments for build file.
Testing context introduced.

 - shared general context containing spark and h2o contexts.
 - specific contexts for local v. distributed tests
scalatest plugin disabled.

Instead of scalatest gradle plugin, plain junit runner
is used.
Do not pass spark.home as null if it is not found in environment.