Don't enable ADB authentication on eng builds

Change-Id: Ibc618e1644080984eb9a409178a2d2bcd76ddf77
diff --git a/config/common.mk b/config/common.mk
index 24ecb2b..8b03b94 100644
--- a/config/common.mk
+++ b/config/common.mk
@@ -69,8 +69,10 @@
     ro.com.android.dateformat=MM-dd-yyyy \
     ro.com.android.dataroaming=false
 
+ifneq ($(TARGET_BUILD_VARIANT),eng)
 # Enable ADB authentication
 ADDITIONAL_DEFAULT_PROPERTIES += ro.adb.secure=1
+endif
 
 # Copy over the changelog to the device
 PRODUCT_COPY_FILES += \