[MINOR] Avoid passing the PermGenSize option to IBM JVMs.

IBM's Java VM doesn't have the concept of a permgen, so this option shouldn't be passed when the vendor property shows it is an IBM JDK.

Author: Tim Ellison <t.p.ellison@gmail.com>
Author: Tim Ellison <tellison@users.noreply.github.com>

Closes #6055 from tellison/MaxPermSize and squashes the following commits:

3a0fb66 [Tim Ellison] Convert tabs back to spaces
6ad4266 [Tim Ellison] Remove unnecessary else clauses to reduce nesting.
d27174b [Tim Ellison] Merge branch 'master' of https://github.com/apache/spark into MaxPermSize
42a8c3f [Tim Ellison] [MINOR] Avoid passing the PermGenSize option to IBM JVMs.

launcher/src/main/java/org/apache/spark/launcher/AbstractCommandBuilder.java

@@ -121,7 +121,10 @@ abstract class AbstractCommandBuilder {
    * set it.
    */
   void addPermGenSizeOpt(List<String> cmd) {
-    // Don't set MaxPermSize for Java 8 and later.
+    // Don't set MaxPermSize for IBM Java, or Oracle Java 8 and later.
+    if (getJavaVendor() == JavaVendor.IBM) {
+      return;
+    }
     String[] version = System.getProperty("java.version").split("\\.");
     if (Integer.parseInt(version[0]) > 1 || Integer.parseInt(version[1]) > 7) {
       return;

launcher/src/main/java/org/apache/spark/launcher/CommandBuilderUtils.java

@@ -32,6 +32,11 @@ class CommandBuilderUtils {
   static final String ENV_SPARK_HOME = "SPARK_HOME";
   static final String ENV_SPARK_ASSEMBLY = "_SPARK_ASSEMBLY";
 
+  /** The set of known JVM vendors. */
+  static enum JavaVendor {
+    Oracle, IBM, OpenJDK, Unknown
+  };
+
   /** Returns whether the given string is null or empty. */
   static boolean isEmpty(String s) {
     return s == null || s.isEmpty();
@@ -108,6 +113,21 @@ class CommandBuilderUtils {
     return os.startsWith("Windows");
   }
 
+  /** Returns an enum value indicating whose JVM is being used. */
+  static JavaVendor getJavaVendor() {
+    String vendorString = System.getProperty("java.vendor");
+    if (vendorString.contains("Oracle")) {
+      return JavaVendor.Oracle;
+    }
+    if (vendorString.contains("IBM")) {
+      return JavaVendor.IBM;
+    }
+    if (vendorString.contains("OpenJDK")) {
+      return JavaVendor.OpenJDK;
+    }
+    return JavaVendor.Unknown;
+  }
+
   /**
    * Updates the user environment, appending the given pathList to the existing value of the given
    * environment variable (or setting it if it hasn't yet been set).