chore(pack-images): use DRYCC_UID DRYCC_GID env

Author: duanhongyi

Dockerfile.build

@@ -16,4 +16,4 @@ RUN cp -rf /var/lib/dpkg /var/lib/dpkg-run; \
   mv /var/lib/dpkg-run /var/lib/dpkg;
 ADD rootfs /
 
-USER drycc
+USER ${DRYCC_UID}

Dockerfile.run

@@ -3,21 +3,20 @@ FROM ${BASE_IMAGE}
 
 ARG STACK_ID
 
-ARG DRYCC_UID=1001
-ARG DRYCC_GID=1001
-ARG DRYCC_HOME_DIR=/workspace
+ENV DRYCC_UID=1001 \
+  DRYCC_GID=1001 \
+  DRYCC_HOME_DIR=/workspace
 
 RUN groupadd drycc --gid ${DRYCC_GID} \
   && useradd drycc -u ${DRYCC_UID} -g ${DRYCC_GID} -s /bin/bash -m -d ${DRYCC_HOME_DIR} \
-  && chown drycc:drycc /opt
-
-USER drycc
+  && chown ${DRYCC_GID}:${DRYCC_UID} /opt
 
+USER ${DRYCC_UID}
+# Pack style, `=` cannot be used
 ENV CNB_USER_ID ${DRYCC_UID}
 ENV CNB_GROUP_ID ${DRYCC_GID}
 ENV CNB_STACK_ID ${STACK_ID}
 ENV CNB_APP_DIR ${DRYCC_HOME_DIR}
-ENV HOME ${DRYCC_HOME_DIR}
 
 LABEL io.buildpacks.stack.id="${STACK_ID}"