CCache doesn't seem to be working -- add this in the entrypoint

utils/docker_entrypoint.sh

@@ -17,6 +17,10 @@ set -e
 if [ -z ${USER_ID+x} ]; then USER_ID=1000; fi
 if [ -z ${GROUP_ID+x} ]; then GROUP_ID=1000; fi
 
+# ccache
+export CCACHE_DIR=/tmp/ccache
+export USE_CCACHE=1
+
 msg="docker_entrypoint: Creating user UID/GID [$USER_ID/$GROUP_ID]" && echo $msg
 groupadd -g $GROUP_ID -r aosp && \
 useradd -u $USER_ID --create-home -r -g aosp aosp