Remove initial Gerrit site from Ubuntu image

Fix the Gerrit site directories removal expansion by
using a temporary bash session. Make sure that the default
image does not contain any initial site data, so that it
can be automatically created at the first execution.

Change-Id: I9dc28a8f316aa4e8597dbf8eaa2c89ead41aab23
diff --git a/ubuntu/20/Dockerfile b/ubuntu/20/Dockerfile
index 1fead56..8d7f810 100644
--- a/ubuntu/20/Dockerfile
+++ b/ubuntu/20/Dockerfile
@@ -19,7 +19,8 @@
 RUN apt-get -y install gerrit=3.3.0.rc2-1 && \
     apt-mark hold gerrit && \
     /entrypoint.sh init && \
-    rm -f /var/gerrit/etc/{ssh,secure}* && rm -Rf /var/gerrit/{static,index,logs,data,index,cache,git,db,tmp}/* && chown -R gerrit:gerrit /var/gerrit
+    bash -c 'rm -f /var/gerrit/etc/{ssh,secure}* && rm -Rf /var/gerrit/{static,index,logs,data,index,cache,git,db,tmp}/*' && \
+    chown -R gerrit:gerrit /var/gerrit
 
 USER gerrit