Tweaks for boot gradle plugin

Fixes gh-152.

... to ease excluding dependencies
eckage changed to bootRepackage

- Register BootRepackage order to use task foo(type: BootRepackage){}
- Allow user to use customConfiguration

configurations {
  hadoopruntime.exclude group: 'log4j'
  hadoopruntime.exclude group: 'org.slf4j'
  hadoopruntime.exclude group: 'org.apache.hadoop'
  hadoopruntime.exclude group: 'org.apache.hive'
  hadoopruntime.exclude group: 'commons-logging'
  hadoopruntime.exclude group: 'org.codehaus.jettison'
  hadoopruntime.exclude group: 'com.thoughtworks.xstream'
}
dependencies {
  compile "org.springframework.batch:spring-batch-core:$springBatchVersion"
  compile "org.springframework.batch:spring-batch-infrastructure:$springBatchVersion"
  compile "org.springframework.data:spring-yarn-batch:$springDataVersion"
  compile "org.springframework.data:spring-yarn-boot:$springDataVersion"
  runtime "org.springframework.data:spring-data-hadoop:$springDataVersion"
  runtime "org.springframework.data:spring-data-hadoop-core:$springDataVersion"
  runtime "log4j:log4j:$log4jVersion"
  runtime "org.slf4j:slf4j-log4j12:$slf4jVersion"
  testCompile "org.springframework.data:spring-yarn-test:$springDataVersion"
  testCompile "org.hamcrest:hamcrest-core:$hamcrestVersion"
  testCompile "org.hamcrest:hamcrest-library:$hamcrestVersion"
  hadoopruntime configurations.runtime
}

springBoot {
  backupSource = true
  customConfiguration = 'hadoopruntime'
}

task appmasterJar(type: Jar) {
  appendix = 'appmaster'
  from sourceSets.main.output
  exclude('**/*Container*')
  exclude('**/*Client*')
}

task clientJar(type: Jar) {
  appendix = 'client'
  from sourceSets.main.output
  exclude('**/*Appmaster*')
  exclude('**/*Container*')
}

task clientBoot(type: BootRepackage, dependsOn: clientJar) {
  withJarTask = clientJar
}

task appmasterBoot(type: BootRepackage, dependsOn: appmasterJar) {
  customConfiguration = "hadoopruntime"
  withJarTask = appmasterJar
}

//jar.enabled = false
//bootRepackage.enabled = false

task bootJars
bootJars.dependsOn = [clientBoot,containerBoot,appmasterBoot]

build.dependsOn(clientBoot)
build.dependsOn(containerBoot)
build.dependsOn(appmasterBoot)
//build.dependsOn(bootJars)
Add build.gradle samples and rename runJar->bootRun