[SPARK-4924] Add a library for launching Spark jobs programatically.

This change encapsulates all the logic involved in launching a Spark job
into a small Java library that can be easily embedded into other applications.

Only the `SparkLauncher` class is supposed to be public in the new launcher
lib, but to be able to use those classes elsewhere in Spark some of the
visibility modifiers were relaxed. This allows us to automate some checks
in unit tests, when before you just had a comment that was easily missed.

A subsequent commit will change Spark core and all the shell scripts to use
this library instead of custom code that needs to be replicated for different
OSes and, sometimes, also in Spark code.

Author: Marcelo Vanzin

launcher/pom.xml

@@ -0,0 +1,77 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Licensed to the Apache Software Foundation (ASF) under one or more
+  ~ contributor license agreements.  See the NOTICE file distributed with
+  ~ this work for additional information regarding copyright ownership.
+  ~ The ASF licenses this file to You under the Apache License, Version 2.0
+  ~ (the "License"); you may not use this file except in compliance with
+  ~ the License.  You may obtain a copy of the License at
+  ~
+  ~    http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  -->
+
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>org.apache.spark</groupId>
+    <artifactId>spark-parent</artifactId>
+    <version>1.3.0-SNAPSHOT</version>
+    <relativePath>../pom.xml</relativePath>
+  </parent>
+
+  <groupId>org.apache.spark</groupId>
+  <artifactId>spark-launcher_2.10</artifactId>
+  <packaging>jar</packaging>
+  <name>Spark Launcher Project</name>
+  <url>http://spark.apache.org/</url>
+  <properties>
+    <sbt.project.name>launcher</sbt.project.name>
+  </properties>
+
+  <dependencies>
+    <!-- NOTE: only test-scope dependencies are allowed in this module. -->
+    <dependency>
+      <groupId>log4j</groupId>
+      <artifactId>log4j</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.scalatest</groupId>
+      <artifactId>scalatest_${scala.binary.version}</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-api</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-log4j12</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <outputDirectory>target/scala-${scala.binary.version}/classes</outputDirectory>
+    <testOutputDirectory>target/scala-${scala.binary.version}/test-classes</testOutputDirectory>
+    <plugins>
+      <plugin>
+        <groupId>org.scalatest</groupId>
+        <artifactId>scalatest-maven-plugin</artifactId>
+        <configuration>
+          <systemProperties>
+            <spark.test.home>${project.basedir}/..</spark.test.home>
+          </systemProperties>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>