[SPARK-6136] [SQL] Removed JDBC integration tests which depends on docker-client

Integration test suites in the JDBC data source (`MySQLIntegration` and `PostgresIntegration`) depend on docker-client 2.7.5, which transitively depends on Guava 17.0. Unfortunately, Guava 17.0 is causing test runtime binary compatibility issues when Spark is compiled against Hive 0.12.0, or Hadoop 2.4.

Considering `MySQLIntegration` and `PostgresIntegration` are ignored right now, I'd suggest moving them from the Spark project to the [Spark integration tests] [1] project. This PR removes both the JDBC data source integration tests and the docker-client test dependency.

[1]: |https://github.com/databricks/spark-integration-tests

<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/apache/spark/4872)
<!-- Reviewable:end -->

Author: Cheng Lian <[email protected]>

Closes #4872 from liancheng/remove-docker-client and squashes the following commits:

1f4169e [Cheng Lian] Removes DockerHacks
159b24a [Cheng Lian] Removed JDBC integration tests which depends on docker-client

Author: liancheng

sql/core/pom.xml

@@ -99,12 +99,6 @@
       <version>9.3-1102-jdbc41</version>
       <scope>test</scope>
     </dependency>
-    <dependency>
-      <groupId>com.spotify</groupId>
-      <artifactId>docker-client</artifactId>
-      <version>2.7.5</version>
-      <scope>test</scope>
-    </dependency>
   </dependencies>
   <build>
     <outputDirectory>target/scala-${scala.binary.version}/classes</outputDirectory>