Pkg test: refactor for readability

builder/startup/generate_container_user

@@ -1,14 +1,13 @@
 detect_libnss_wrapper() {
   if $(which dpkg &>/dev/null); then
     libnss_wrapper_file=$(dpkg -S libnss_wrapper.so | awk -F' ' '{ print $2 }')
-    LD_PRELOAD="$libnss_wrapper_file"
     return
   fi
 
   if [ -r /usr/lib/libnss_wrapper.so ]; then
-      LD_PRELOAD=/usr/lib/libnss_wrapper.so
+      libnss_wrapper_file=/usr/lib/libnss_wrapper.so
   elif [ -r /usr/lib64/libnss_wrapper.so ]; then
-      LD_PRELOAD=/usr/lib64/libnss_wrapper.so
+      libnss_wrapper_file=/usr/lib64/libnss_wrapper.so
   else
       echo "no libnss_wrapper.so installed!"
       exit 1
@@ -42,6 +41,6 @@ if [ x"$USER_ID" != x"0" ]; then
     export NSS_WRAPPER_GROUP
 
     detect_libnss_wrapper
-    echo "nss_wrapper location: $LD_PRELOAD"
+    echo "nss_wrapper location: $libnss_wrapper_file"
-    export LD_PRELOAD
+    export LD_PRELOAD="$libnss_wrapper_file"
 fi