[FLINK-6965] Include snappy-java in flink-dist

This closes #4160.

flink-core/pom.xml

@@ -79,13 +79,12 @@ under the License.
 		<dependency>
 			<groupId>org.apache.avro</groupId>
 			<artifactId>avro</artifactId>
-			<!-- managed version -->
-			<exclusions>
-				<exclusion>
-					<groupId>org.xerial.snappy</groupId>
-					<artifactId>snappy-java</artifactId>
-				</exclusion>
-			</exclusions>
+		</dependency>
+
+		<!-- We explicitly depend on snappy since connectors that require it load it through the system class loader -->
+		<dependency>
+			<groupId>org.xerial.snappy</groupId>
+			<artifactId>snappy-java</artifactId>
 		</dependency>
 
 		<!-- ASM is needed for type extraction -->

pom.xml

@@ -267,6 +267,12 @@ under the License.
 				<version>1.8.2</version>
 			</dependency>
 
+			<dependency>
+				<groupId>org.xerial.snappy</groupId>
+				<artifactId>snappy-java</artifactId>
+				<version>1.1.1.3</version>
+			</dependency>
+
 			<!-- Make sure we use a consistent commons-cli version throughout the project -->
 			<dependency>
 				<groupId>commons-cli</groupId>

tools/travis_mvn_watchdog.sh

@@ -165,7 +165,7 @@ watchdog () {
 	done
 }
 
-# Check the final fat jar for illegal artifacts
+# Check the final fat jar for illegal or missing artifacts
 check_shaded_artifacts() {
 	jar tf build-target/lib/flink-dist*.jar > allClasses
 	ASM=`cat allClasses | grep '^org/objectweb/asm/' | wc -l`
@@ -184,6 +184,13 @@ check_shaded_artifacts() {
 		exit 1
 	fi
 
+	SNAPPY=`cat allClasses | grep '^org/xerial/snappy' | wc -l`
+	if [ $SNAPPY == "0" ]; then
+		echo "=============================================================================="
+		echo "Missing snappy dependencies in fat jar"
+		echo "=============================================================================="
+		exit 1
+	fi
 }
 
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