[SPARK-16796][WEB UI] Visible passwords on Spark environment page

## What changes were proposed in this pull request?

Mask spark.ssl.keyPassword, spark.ssl.keyStorePassword, spark.ssl.trustStorePassword in Web UI environment page.
(Changes their values to ***** in env. page)

## How was this patch tested?

I've built spark, run spark shell and checked that this values have been masked with *****.

Also run tests:
./dev/run-tests

[info] ScalaTest
[info] Run completed in 1 hour, 9 minutes, 5 seconds.
[info] Total number of tests run: 2166
[info] Suites: completed 65, aborted 0
[info] Tests: succeeded 2166, failed 0, canceled 0, ignored 590, pending 0
[info] All tests passed.

![mask](https://cloud.githubusercontent.com/assets/15244468/17262154/7641e132-55e2-11e6-8a6c-30ead77c7372.png)

Author: Artur Sukhenko <[email protected]>

Closes #14409 from Devian-ua/maskpass.

(cherry picked from commit 3861273)
Signed-off-by: Sean Owen <[email protected]>

Author: Devian-ua

core/src/main/scala/org/apache/spark/ui/env/EnvironmentPage.scala

@@ -26,11 +26,15 @@ import org.apache.spark.ui.{UIUtils, WebUIPage}
 private[ui] class EnvironmentPage(parent: EnvironmentTab) extends WebUIPage("") {
   private val listener = parent.listener
 
+  private def removePass(kv: (String, String)): (String, String) = {
+    if (kv._1.toLowerCase.contains("password")) (kv._1, "******") else kv
+  }
+
   def render(request: HttpServletRequest): Seq[Node] = {
     val runtimeInformationTable = UIUtils.listingTable(
       propertyHeader, jvmRow, listener.jvmInformation, fixedWidth = true)
     val sparkPropertiesTable = UIUtils.listingTable(
-      propertyHeader, propertyRow, listener.sparkProperties, fixedWidth = true)
+      propertyHeader, propertyRow, listener.sparkProperties.map(removePass), fixedWidth = true)
     val systemPropertiesTable = UIUtils.listingTable(
       propertyHeader, propertyRow, listener.systemProperties, fixedWidth = true)
     val classpathEntriesTable = UIUtils.listingTable(