Fixing installation of preprocessor dependencies

preprocessor/Dockerfile

@@ -35,7 +35,8 @@ LABEL name="prism view server preprocessor" \
 
 USER root
 
-RUN apt install -y \
+RUN apt update && \
+    apt install -y \
         python3-redis python3-keystoneclient python3-swiftclient wait-for-it && \
     apt autoremove -y && \
     apt clean && \