[Gradle] add pre-action, post-action

prepostaction.gradle

task mytask {
    doFirst {
        println "doFirst"
    }
}
mytask.doLast {
    println "doLast"
}
mytask << {
    println "doLast by <<" // this is same as mytask.doLast {}
}

// add action to existing task
check.doFirst {
    println "doFirst for check!"
}

check.doLast {
    println "doLast for check!"
}