Clone a git repo into a specific subdir.

git-clone-into-subdir.groovy

checkout([
	$class: 'GitSCM',
	branches: [
	    [name: '*/branchname']
	],
	doGenerateSubmoduleConfigurations: false,
	extensions: [
	    [
	    	$class: 'RelativeTargetDirectory',
	    	relativeTargetDir: 'MyDirectory'
	    ]
	],
	submoduleCfg: [],
	userRemoteConfigs: [
	    [
	    	credentialsId: 'myId',
	    	url: 'https://github.com/jenkinsci/jenkins.git'
	    ]
	]
])