[SPARK-4298][Core] - The spark-submit cannot read Main-Class from Manifest.

Resolves a bug where the `Main-Class` from a .jar file wasn't being read in properly. This was caused by the fact that the `primaryResource` object was a URI and needed to be normalized through a call to `.getPath` before it could be passed into the `JarFile` object.

Author: Brennon York <brennon.york@capitalone.com>

Closes #3561 from brennonyork/SPARK-4298 and squashes the following commits:

5e0fce1 [Brennon York] Use string interpolation for error messages, moved comment line from original code to above its necessary code segment
14daa20 [Brennon York] pushed mainClass assignment into match statement, removed spurious spaces, removed { } from case statements, removed return values
c6dad68 [Brennon York] Set case statement to support multiple jar URI's and enabled the 'file' URI to load the main-class
8d20936 [Brennon York] updated to reset the error message back to the default
a043039 [Brennon York] updated to split the uri and jar vals
8da7cbf [Brennon York] fixes SPARK-4298

(cherry picked from commit 8e14c5e)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>

Conflicts:
	core/src/main/scala/org/apache/spark/deploy/SparkSubmitArguments.scala

Author: Brennon York

core/src/main/scala/org/apache/spark/deploy/SparkSubmitArguments.scala

@@ -19,6 +19,7 @@ package org.apache.spark.deploy
 
 import java.io.{File, FileInputStream, IOException}
 import java.util.Properties
+import java.net.URI
 import java.util.jar.JarFile
 
 import scala.collection.JavaConversions._
@@ -126,14 +127,23 @@ private[spark] class SparkSubmitArguments(args: Seq[String], env: Map[String, St
 
     // Try to set main class from JAR if no --class argument is given
     if (mainClass == null && !isPython && primaryResource != null) {
-      try {
-        val jar = new JarFile(primaryResource)
-        // Note that this might still return null if no main-class is set; we catch that later
-        mainClass = jar.getManifest.getMainAttributes.getValue("Main-Class")
-      } catch {
-        case e: Exception =>
-          SparkSubmit.printErrorAndExit("Cannot load main class from JAR: " + primaryResource)
-          return
+      val uri = new URI(primaryResource)
+      val uriScheme = uri.getScheme()
+
+      uriScheme match {
+        case "file" =>
+          try {
+            val jar = new JarFile(uri.getPath)
+            // Note that this might still return null if no main-class is set; we catch that later
+            mainClass = jar.getManifest.getMainAttributes.getValue("Main-Class")
+          } catch {
+            case e: Exception =>
+              SparkSubmit.printErrorAndExit(s"Cannot load main class from JAR $primaryResource")
+          }
+        case _ =>
+          SparkSubmit.printErrorAndExit(
+            s"Cannot load main class from JAR $primaryResource with URI $uriScheme. " +
+            "Please specify a class through --class.")
       }
     }