Update plasma/Dockerfile

plasma/Dockerfile

@@ -2,6 +2,9 @@
 FROM alpine/base
 USER root
 
+# Build ARG: use "root" for debugging
+ARG debug
+
 # X session environment variable
 ENV STARTXBIN=startplasma-x11
 
@@ -16,5 +19,5 @@ RUN apk add --no-cache \
 # Tigervnc initialization scripts
 COPY *.sh /app/init.d/
 
-# Reset user home directory
-USER user
+# Default environment
+USER ${debug:-user}