Allow variables when importing shared pipelines

[Jefferson Fermo]

Hi, 

  Is there a way to be able to use variables ${{}} when using imported pipelines, this is to allow us to easily roll forward/backward versions of our shared pipeline?

pipelines:
  custom:
    release_start:
      import: maven_shared_bitbucket_pipelines:${{MAVEN_SHARED_BITBUCKET_PIPELINES_VERSION}}:release_start

Regards,

jeff