Use this command in your proguard-rules.pro file:
-printmapping path/to/your/file/file_name.txt
the file will be written in part {root}/path/to/your/file  with file_name.txt name.
If you want to have different setting for different flavors you can define many proguard-rules for them
I found one more idea but I am not sure that it is right way. 
You can define your path in flavors:
productFlavors {
    test1 {
        applicationId "com.android.application.test"
        project.ext."${name}Path" = 'path/one/mapp.txt'
    }
    test2 {
        project.ext."${name}Path" = 'path/two/mapp.txt'
    }
}
And as next you can define new task before $asseble{variant.name.capitalize()} task as is shown below:
android.applicationVariants.all { variant ->
    def envFlavor = variant.productFlavors.get(0).name
    def modifyProguardPath = tasks.create(name: "modifyProguardFor${variant.name.capitalize()}", type: Exec) {
        def pathToMap = project."${envFlavor}Test1"
        doFirst {
            println "==== Edit start: $pathToMap ===="
        }
        doLast {
            println "==== Edit end: $pathToMap ===="
        }
        executable "${rootDir}/utils/test.bash"
        args pathToMap
    }
    project.tasks["assemble${variant.name.capitalize()}"].dependsOn(modifyProguardPath);
}
and in script ${root}/utils/test.bash - you can modify proguard-rules.pro.
But I think that exist better solution.