Allow for plugin testing.

[matschaffer]

With this change in place you can include plugin specs in grunt test by creating a src/config.js like that includes something like this:

      plugins: {
        // list of plugin panels
        panels: [],
        // requirejs modules in plugins folder that should be loaded
        // for example custom datasources
        dependencies: ['grafana-plugins/atlas.Datasource'],
        specs: ['grafana-plugins/specs/atlasDatasource-specs']
      }

[matschaffer]

The large-sized change was due to some issues I hit trying to use helper.js from both a plugin spec and the regular specs. Seems that asking require to load the same file from two different paths causes a load time out. Injecting the helper got around this.

[coveralls]

Coverage remained the same when pulling 85e50ec on matschaffer:plugin-spec-support into 32ae0ea on grafana:master.

[torkelo]

This looks great! Will merge tomorrow if I can find the time!