[docker] Fix running docker container with existing volume

- Print some useful info message in the `entrypoint.sh` script file.
- If the `workspace` directory already exists when the container started, try
to run the given command with the owner of the workspace directory, otherwise
run it with the `codechecker` user.

web/docker/entrypoint.sh

@@ -1,29 +1,41 @@
 #!/bin/bash
 
-USER_ID=$($USER)
+USER_ID="$(id -u)"
 USER_GROUP="$(id -g)"
 WORKSPACE_DIR="/workspace"
 PGPASS_FILE=$WORKSPACE_DIR/.pgpass
 
-if [ "$(id -u)" = '0' ]; then
-  # Create workspace directory and change the permission to 'codechecker' user
-  # if this directory doesn't exists.
-  if [ ! -d $WORKSPACE_DIR ]; then
+if [ "$USER_ID" = '0' ]; then
+  echo "Container started with 'root' user."
+
+  if [ -d $WORKSPACE_DIR ]; then
+    echo "Workspace directory '${WORKSPACE_DIR}' already exists."
+
+    workspace_dir_owner=$(stat ${WORKSPACE_DIR} -c %u)
+    if [ "${workspace_dir_owner}" != '0' ]; then
+      echo "Executing script with workspace directory owner (UID): '${workspace_dir_owner}'..."
+      exec gosu $workspace_dir_owner "$0" "$@"
+    fi
+  else
+    echo "Creating workspace directory: '${WORKSPACE_DIR}'."
+    echo "WARNING: This directory exists ONLY within the containter!"
+
     mkdir -p $WORKSPACE_DIR
     chown -R codechecker:codechecker $WORKSPACE_DIR
-  fi
 
-  # Execute this script again with codechecker user.
-  exec gosu codechecker "$0" "$@"
+    echo "Executing script with internal 'codechecker' user (UID: $(id -u codechecker))..."
+    exec gosu codechecker "$0" "$@"
+  fi
 fi
 
-# Set PostgreSQL password file from secrets.
 pgpass=/run/secrets/pgpass
 if [ -f $pgpass ]; then
+  echo "Set PostgreSQL password file from secrets."
   cat $pgpass > ${PGPASS_FILE}
   chmod 0600 ${PGPASS_FILE}
   chown ${USER_ID}:${USER_GROUP} ${PGPASS_FILE}
   export PGPASSFILE=${PGPASS_FILE}
 fi
 
+echo "Executing command: '$@'."
 exec "$@"