[SPARK-10575] [SPARK CORE] Wrapped RDD.takeSample with Scope

Remove return statements in RDD.takeSample and wrap it withScope

Author: vinodkc <vinod.kc.in@gmail.com>
Author: vinodkc <vinodkc@users.noreply.github.com>
Author: Vinod K C <vinod.kc@huawei.com>

Closes #8730 from vinodkc/fix_takesample_return.