Build: Add support for specifying build variant in brunch/breakfast

This little modification allows specifying build variant in brunch/breakfast commands. For example we can use "brunch i9300 user" to build user variant instead of default userdebug.

When no extra argument is given, userdebug is default.

Change-Id: I2d438209f8a14949c64baa66485c811da384d20b
diff --git a/build/envsetup.sh b/build/envsetup.sh
index a4fd76b..284c9ae 100644
--- a/build/envsetup.sh
+++ b/build/envsetup.sh
@@ -212,6 +212,7 @@
 function breakfast()
 {
     target=$1
+    local variant=$2
     BLISS_DEVICES_ONLY="true"
     unset LUNCH_MENU_CHOICES
     add_lunch_combo full-eng
@@ -232,7 +233,10 @@
             lunch $target
         else
             # This is probably just the bliss model name
-            lunch bliss_$target-userdebug
+            if [ -z "$variant" ]; then
+                variant="userdebug"
+            fi
+            lunch bliss_$target-$variant
         fi
     fi
     return $?