Switching back to Pig version 0.13.0 due to SHDP-454
SHDP-454 Fix test failures for Pig 0.14.0

- update Pig to 0.14.0 for Hadoop 2.6.x
SHDP-450 Change docs to asciidoc

- Conversion from docbook to asciidoc
- Gradle updated from 1.8 to 2.2.1 to
  get asciidoc plugins working.