Added task to execute multiple oc commands (#92)

[lstocchi]

It fixes #92

With this PR users can now add multiple oc commands with a single task without creating multiple single-command tasks into a pipeline.

Example below:

- task: oc-list-cmds@2
  inputs:
    openshiftService: 'My Openshift'
    version: 'v3.11.0'
    cmds: |
          'oc version
          oc get pods          
          oc get dc' 

Currently there is no json helper support. Once #93 will be approved, it will be included into this task as well.