SiteLibraryLoaderUtil: catch NoSuchFileException when scanning for JARs

Without this, a stack trace is emitted to the console log. This causes
a lot of noise particularly when running acceptance tests in Eclipse
because it is emitted on every test.

See [1] for an example of the stack trace.

[1] http://paste.openstack.org/show/182219/

Change-Id: I1624f6a6aa42ae73ae1e97d1cb53d593184567ab
diff --git a/gerrit-common/src/main/java/com/google/gerrit/common/SiteLibraryLoaderUtil.java b/gerrit-common/src/main/java/com/google/gerrit/common/SiteLibraryLoaderUtil.java
index 24451a4..2511a51 100644
--- a/gerrit-common/src/main/java/com/google/gerrit/common/SiteLibraryLoaderUtil.java
+++ b/gerrit-common/src/main/java/com/google/gerrit/common/SiteLibraryLoaderUtil.java
@@ -17,6 +17,7 @@
 import static com.google.gerrit.common.FileUtil.lastModified;
 
 import com.google.common.collect.ComparisonChain;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Ordering;
 
 import org.slf4j.Logger;
@@ -25,6 +26,7 @@
 import java.io.IOException;
 import java.nio.file.DirectoryStream;
 import java.nio.file.Files;
+import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
 import java.util.List;
 
@@ -60,6 +62,8 @@
               .result();
         }
       }.sortedCopy(jars);
+    } catch (NoSuchFileException nsfe) {
+      return ImmutableList.of();
     }
   }