Add ability to execute various custom maven executions when using the XWiki pipeline library

parallel(
    "standard": {
        node {
            xwikiBuild {
                xvnc = false
                goals = "clean"
            }
        }
    },
    "test": {
        node {
            xwikiBuild {
                xvnc = false
                goals = "clean"
            }
        }
    }
)

node {
  xwikiBuild {
    xvnc = false
    goals = "clean"
  }
}

xwikiModule {
  xvnc = false
  goals = "clean"
}