- deny all globals that are not hases and doesn't contain script, the script is required now
- verify that script is either string or array of an strings

Support yaml variables

This MR introduces ability to define variables from YAML.

```yaml
variables:
  DB_NAME: postgres

test:
  script: echo $DB_NAME
```

The variables are passed using the same API as Secure Variables. The API introduces additional parameter: public. All variables defined in YAML are marked as public. The GitLab Runner when detects public variables will pass them to the services. This makes it easy to fine tune linked services to for example define database name.

```yaml
services:
- postgres

variables:
  POSTGRES_DB: gitlab
```

The above example will run [postgres](https://registry.hub.docker.com/u/library/postgres/) and pass POSTGRES_DB to postgres container making it to create `gitlab` database instead of default `postges`.

**Note:** All variables will passed to all service containers. It's not designed to distinguish which variable should go where.

/cc @sytses @vsizov @dzaporozhets 

See merge request !227

Fix service testing

Fixes:
- https://gitlab.com/gitlab-org/gitlab-ci/issues/248
- https://gitlab.com/gitlab-org/gitlab-ci/issues/208

/cc @vsizov 

See merge request !221

Commits with [ci skip] have special skipped status

![Screen_Shot_2015-07-30_at_14.02.50](https://gitlab.com/gitlab-org/gitlab-ci/uploads/f200af385679b564cd15d730bd4ccd20/Screen_Shot_2015-07-30_at_14.02.50.png)

+ Commits with [ci skip] are marked as skipped
+ Commits without builds are marked as skipped

Resolution for:
+ https://dev.gitlab.org/gitlab/gitlab-ci/issues/264
+ https://dev.gitlab.org/gitlab/gitlab-ci/issues/266

This requires CE update:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/1073

/cc @vsizov @sytses 

See merge request !216