Update server_jre.sls

Added the ability to override needing to download java into the salt repo, allow java to be downloaded automatically
Merge pull request #1 from auser/patch-1

Update server_jre.sls
Update README.rst

Added documentation for java in the pillar
Merge pull request #2 from auser/patch-2

Update README.rst
Updated so you can define jre and java
Added jdk as an option, updated readme with the format