[SPARK-7926] [PYSPARK] use the official Pyrolite release

Switch to the official Pyrolite release from the one published under `org.spark-project`. Thanks irmen for making the releases on Maven Central. We didn't upgrade to 4.6 because we don't have enough time for QA. I excludes `serpent` from its dependencies because we don't use it in Spark.
~~~
[info]   +-net.jpountz.lz4:lz4:1.3.0
[info]   +-net.razorvine:pyrolite:4.4
[info]   +-net.sf.py4j:py4j:0.8.2.1
~~~

davies

Author: Xiangrui Meng <meng@databricks.com>

Closes #6472 from mengxr/SPARK-7926 and squashes the following commits:

7b3c6bf [Xiangrui Meng] use the official Pyrolite release

core/pom.xml

@@ -377,9 +377,15 @@
       <scope>test</scope>
     </dependency>
     <dependency>
-      <groupId>org.spark-project</groupId>
+      <groupId>net.razorvine</groupId>
       <artifactId>pyrolite</artifactId>
       <version>4.4</version>
+      <exclusions>
+        <exclusion>
+          <groupId>net.razorvine</groupId>
+          <artifactId>serpent</artifactId>
+        </exclusion>
+      </exclusions>
     </dependency>
     <dependency>
       <groupId>net.sf.py4j</groupId>