Add a '-l' shortcut for --log-level-display.

Change-Id: Ic55578599a2de275672f668b542d77ffda777900
diff --git a/src/com/android/tradefed/log/FileLogger.java b/src/com/android/tradefed/log/FileLogger.java
index 1995a01..50b9303 100644
--- a/src/com/android/tradefed/log/FileLogger.java
+++ b/src/com/android/tradefed/log/FileLogger.java
@@ -49,7 +49,7 @@
             + LogUtil.LOG_LEVEL_LIST + ".")
     private String mLogLevel = LogLevel.DEBUG.getStringValue();
 
-    @Option(name = "log-level-display", description =
+    @Option(name = "log-level-display", shortName = 'l', description =
         "the minimum log level to display on stdout. Must be one of " + LogUtil.LOG_LEVEL_LIST +
         ".", importance = Importance.ALWAYS)
     private String mLogLevelStringDisplay = LogLevel.ERROR.getStringValue();