how append date build to versionNameSuffix on gradle

I am using Android Studio and I need to append a suffix to the versionNameSuffix on my Android build.gradle file. I have three different build types and I only need to append the datetime to my "beta" release. My actual file is:

defaultConfig {
    versionCode 14
    versionName "0.7.5"
    minSdkVersion 9
    targetSdkVersion 18
}
buildTypes {
    beta {
        packageNameSuffix ".beta"
        versionNameSuffix "-beta"
        signingConfig signingConfigs.debug
    }
    ....
}

For testing and automatic deploy, I need to get a final versionName like: 0.7.5-beta-build20131004, 0.7.5-beta-build1380855996 or something like that. Any ideas?

beta {
    packageNameSuffix ".beta"
    versionNameSuffix "-beta" + "-build" + getDate()
    signingConfig signingConfigs.debug
}

def getDate() {
    def date = new Date()
    def formattedDate = date.format('yyyyMMddHHmmss')
    return formattedDate
}

Condensed:

def getDate() {
    return new Date().format('yyyyMMddHHmmss')
}

You can define in your build.gradle custom functions and variables.

def versionMajor = 3

def buildTime() {
    def df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm'Z'") // you can change it
    df.setTimeZone(TimeZone.getTimeZone("UTC"))
    return df.format(new Date())
}

Then you can use it:

android {
    defaultConfig {
       versionName "${versionMajor}-beta-build-${buildTime()}"
    }
}

or if you want to add it in you versionNameSuffix

beta {
    versionNameSuffix "-beta-build-${buildTime()}"      
}