ext4_utils: simg2img: Add LOCAL_MODULE_TAGS in Android.mk

1) simg2img was being installed on the device.  For the
BUILD_EXECUTABLE add an "optional" tag (instead of the implied
default of "user") so this does not happen.

2) In preparation of removing simg2img from user_tags.mk, add a
"debug" tag to the BUILD_HOST_EXECUTABLE so it will be put in the
host bin subdirectory for eng and userdebug builds.

Change-Id: Ib8407e366b8154772e3b78cabb09655851ce77de
Signed-off-by: Scott Anderson <saa@android.com>
diff --git a/ext4_utils/Android.mk b/ext4_utils/Android.mk
index f09197c..4819a9a 100644
--- a/ext4_utils/Android.mk
+++ b/ext4_utils/Android.mk
@@ -93,6 +93,7 @@
 LOCAL_SRC_FILES := simg2img.c \
 	sparse_crc32.c
 LOCAL_MODULE := simg2img
+LOCAL_MODULE_TAGS := debug
 
 include $(BUILD_HOST_EXECUTABLE)
 
@@ -101,6 +102,7 @@
 LOCAL_SRC_FILES := simg2img.c \
 	sparse_crc32.c
 LOCAL_MODULE := simg2img
+LOCAL_MODULE_TAGS := optional
 
 include $(BUILD_EXECUTABLE)