Reverted removal of validation relativeSD<0.000017

Author: Vinod K C

python/pyspark/rdd.py

@@ -2237,6 +2237,8 @@ def countApproxDistinct(self, relativeSD=0.05):
         >>> 16 < n < 24
         True
         """
+        if relativeSD < 0.000017:
+            raise ValueError("relativeSD should be greater than 0.000017")
         # the hash space in Java is 2^32
         hashRDD = self.map(lambda x: portable_hash(x) & 0xFFFFFFFF)
         return hashRDD._to_java_object_rdd().countApproxDistinct(relativeSD)