[SPARK-9001] Fixing errors in javadocs that lead to failed build/sbt doc

These are minor corrections in the documentation of several classes that are preventing:

```bash
build/sbt publish-local
```

I believe this might be an issue associated with running JDK8 as ankurdave does not appear to have this issue in JDK7.

Author: Joseph Gonzalez <joseph.e.gonzalez@gmail.com>

Closes #7354 from jegonzal/FixingJavadocErrors and squashes the following commits:

6664b7e [Joseph Gonzalez] making requested changes
2e16d89 [Joseph Gonzalez] Fixing errors in javadocs that prevents build/sbt publish-local from completing.

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

@@ -25,11 +25,12 @@ import java.util.Map;
 
 import static org.apache.spark.launcher.CommandBuilderUtils.*;
 
-/**
+/** 
  * Launcher for Spark applications.
- * <p/>
+ * <p>
  * Use this class to start Spark applications programmatically. The class uses a builder pattern
  * to allow clients to configure the Spark application and launch it as a child process.
+ * </p>
  */
 public class SparkLauncher {
 

launcher/src/main/java/org/apache/spark/launcher/package-info.java

@@ -17,13 +17,17 @@
 
 /**
  * Library for launching Spark applications.
- * <p/>
+ * 
+ * <p>
  * This library allows applications to launch Spark programmatically. There's only one entry
  * point to the library - the {@link org.apache.spark.launcher.SparkLauncher} class.
- * <p/>
+ * </p>
+ *
+ * <p>
  * To launch a Spark application, just instantiate a {@link org.apache.spark.launcher.SparkLauncher}
  * and configure the application to run. For example:
- *
+ * </p>
+ * 
  * <pre>
  * {@code
  *   import org.apache.spark.launcher.SparkLauncher;

unsafe/src/main/java/org/apache/spark/unsafe/bitset/BitSet.java

@@ -90,7 +90,7 @@ public final class BitSet {
    * To iterate over the true bits in a BitSet, use the following loop:
    * <pre>
    * <code>
-   *  for (long i = bs.nextSetBit(0); i >= 0; i = bs.nextSetBit(i + 1)) {
+   *  for (long i = bs.nextSetBit(0); i &gt;= 0; i = bs.nextSetBit(i + 1)) {
    *    // operate on index i here
    *  }
    * </code>

unsafe/src/main/java/org/apache/spark/unsafe/bitset/BitSetMethods.java

@@ -87,7 +87,7 @@ public final class BitSetMethods {
    * To iterate over the true bits in a BitSet, use the following loop:
    * <pre>
    * <code>
-   *  for (long i = bs.nextSetBit(0, sizeInWords); i >= 0; i = bs.nextSetBit(i + 1, sizeInWords)) {
+   *  for (long i = bs.nextSetBit(0, sizeInWords); i &gt;= 0; i = bs.nextSetBit(i + 1, sizeInWords)) {
    *    // operate on index i here
    *  }
    * </code>

unsafe/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java

@@ -404,14 +404,17 @@ public final class BytesToBytesMap {
      * at the value address.
      * <p>
      * It is only valid to call this method immediately after calling `lookup()` using the same key.
+     * </p>
      * <p>
      * The key and value must be word-aligned (that is, their sizes must multiples of 8).
+     * </p>
      * <p>
      * After calling this method, calls to `get[Key|Value]Address()` and `get[Key|Value]Length`
      * will return information on the data stored by this `putNewKey` call.
+     * </p>
      * <p>
      * As an example usage, here's the proper way to store a new key:
-     * <p>
+     * </p>
      * <pre>
      *   Location loc = map.lookup(keyBaseObject, keyBaseOffset, keyLengthInBytes);
      *   if (!loc.isDefined()) {
@@ -420,6 +423,7 @@ public final class BytesToBytesMap {
      * </pre>
      * <p>
      * Unspecified behavior if the key is not defined.
+     * </p>
      */
     public void putNewKey(
         Object keyBaseObject,

unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java

@@ -330,8 +330,8 @@ public final class UTF8String implements Comparable<UTF8String>, Serializable {
   /**
    * Returns str, right-padded with pad to a length of len
    * For example:
-   *   ('hi', 5, '??') => 'hi???'
-   *   ('hi', 1, '??') => 'h'
+   *   ('hi', 5, '??') =&gt; 'hi???'
+   *   ('hi', 1, '??') =&gt; 'h'
    */
   public UTF8String rpad(int len, UTF8String pad) {
     int spaces = len - this.numChars(); // number of char need to pad
@@ -363,8 +363,8 @@ public final class UTF8String implements Comparable<UTF8String>, Serializable {
   /**
    * Returns str, left-padded with pad to a length of len.
    * For example:
-   *   ('hi', 5, '??') => '???hi'
-   *   ('hi', 1, '??') => 'h'
+   *   ('hi', 5, '??') =&gt; '???hi'
+   *   ('hi', 1, '??') =&gt; 'h'
    */
   public UTF8String lpad(int len, UTF8String pad) {
     int spaces = len - this.numChars(); // number of char need to pad