Added cartridges:lint rake task and YAML schema for manifest.yaml

This path will add 'rake cartridges:lint' task, which should validate the syntax of all cartridge manifest.yml files.
For this, I use [kwalify|http://www.kuwata-lab.com/kwalify] YAML validator. The output of this rake task looks like this:

```
 ~/code/origin-server → rake cartridges:lint
[openshift-origin-cartridge-haproxy/metadata/manifest.yml] VALID.
[openshift-origin-cartridge-ruby/metadata/manifest.yml.rhel] VALID.
[openshift-origin-cartridge-ruby/metadata/manifest.yml.f19] VALID.
[openshift-origin-cartridge-postgresql/metadata/manifest.yml.rhel] VALID.
[openshift-origin-cartridge-postgresql/metadata/manifest.yml.f19] VALID.
[openshift-origin-cartridge-mock-plugin/metadata/manifest.yml] VALID.
[openshift-origin-cartridge-mock/metadata/manifest.yml] VALID.
[openshift-origin-cartridge-switchyard/metadata/manifest.yml] VALID.
[openshift-origin-cartridge-diy/metadata/manifest.yml] VALID.
[openshift-origin-cartridge-jbossews/metadata/manifest.yml] VALID.
openshift-origin-cartridge-10gen-mms-agent/metadata/manifest.yml: INVALID
  - [/] key 'License:' is required.
[openshift-origin-cartridge-jbosseap/metadata/manifest.yml] VALID.
[openshift-origin-cartridge-perl/metadata/manifest.yml.rhel] VALID.
[openshift-origin-cartridge-perl/metadata/manifest.yml.f19] VALID.
[openshift-origin-cartridge-cron/metadata/manifest.yml] VALID.
[openshift-origin-cartridge-mysql/metadata/manifest.yml] VALID.
[openshift-origin-cartridge-nodejs/metadata/manifest.yml.rhel] VALID.
[openshift-origin-cartridge-nodejs/metadata/manifest.yml.fedora] VALID.
[openshift-origin-cartridge-python/metadata/manifest.yml.rhel] VALID.
[openshift-origin-cartridge-python/metadata/manifest.yml.f19] VALID.
[openshift-origin-cartridge-phpmyadmin/metadata/manifest.yml.rhel] VALID.
[openshift-origin-cartridge-phpmyadmin/metadata/manifest.yml.f19] VALID.
[openshift-origin-cartridge-mongodb/metadata/manifest.yml] VALID.
[openshift-origin-cartridge-jbossas/metadata/manifest.yml] VALID.
[openshift-origin-cartridge-jenkins/metadata/manifest.yml] VALID.
[openshift-origin-cartridge-mariadb/metadata/manifest.yml] VALID.
[openshift-origin-cartridge-php/metadata/manifest.yml.rhel] VALID.
[openshift-origin-cartridge-php/metadata/manifest.yml.fedora19] VALID.
openshift-origin-cartridge-jenkins-client/metadata/manifest.yml: INVALID
  - [/] key 'Vendor:' is required.
```