Install Oracle JDK8-EA from Webupd8 PPA
Webupd8 PPA fully supports 'update-alternatives'

This is a "documentation" commit to show that *.jinfo files are now well
handled in Webupd8 packages. These files are therefore no more needed to
be deployed by Chef recipes and they will be removed in next commit.
Use default 'update-alternatives' packaging

- Remove obsolete .jinfo files for Oracle JDK7 and JDK8, since Webupd8
  packages configure 'alternatives' well
- Clean OpenJDK7 recipe, since Ubuntu package configure 'alternative'
  well on 12.04 (compatible with jdk_switcher alias)
- At the end, ensure that OpenJDK7 (hardcoded for now) is set as default java version

For the records, see in particular:
- 13687ce08ff8083aff1ffac442290a455681b586
- 04017c478168ba7a42a74ac3b9ec0a9885f368b2
- 139b3d8c04522959ce90607f35d75521db9da222
Use Ubuntu Java keystore for all JDKs

This way we ensure that:
- all java runtime will behave the same, independently of selected JDK
- most common SSL CA will be supported (including popular authorities like
  StartSSL, ...)

Notes:

clojars.org now uses certificate issued by RapidSSL CA, and I
verified that default keystore provided by Webupd8 packages also work
fine to run Leiningen2. But as argumented above, for any other similar
possible use case, it is safer to use the certificates provided by
Ubuntu packaging.

The current implementation will auto-install an openjdk6 JRE as
dependency of the package ca-certificates-java. This is not *ideal*, but
it should have no impact. As a variant, we could provision a static copy
of the ubuntu keystore file, via cookbook_file or remote_file.
Remove obsolete java.seed file

No more needed with recent versions of Webupd8 packages.
Java cookbook only supports Ubuntu 12.04+

Remove outdated README.md and obsolete/unused pieces of code. This
will make cookbook more readable and easier to maintain. We'll have time
to refactor back the day we want to support more linux flavors :)

Note that tzdata workaround (65b0ecaaf04b1a60bc463077222a1e046391f333) is kept
untouched (just the package installation statements that are written a
bit differently).
Refactor java attributes and recipes

Attention: the 'multi' recipe must not be directly called, since it is
now conditionally included by 'default' recipe (depending on
'alternate_versions' value). travis-images run_list for JVM and Ruby
must be hence updated.
Install IcedTea plugin for OpenJDK 6 and 7

With this change, jdk_switcher (update-java-alternatives) won't warn anymore about
plugin alternative that does not exist (/usr/lib/jvm/java-7-openjdk-amd64/jre/lib/amd64/IcedTeaPlugin.so)
Add a comment about missing JCE in JDK8-EA edition
Update java/metadata.rb about multi refactoring
Improve jdk_switcher

- provision as template to ensure that both 'default' versions match
- print more warnings when an unsupported version name is requested.
  See also michaelklishin/jdk_switcher#2
java: synchronize jdk_switcher.sh with upstream
Merge pull request #236 from gildegoma/revamp-java-and-add-oraclejdk8

Revamp Java cookbook and add support for Oracle JDK8 (EA Edition)