Pkg test: use dpkg to find libnss_wrapper.so

builder/startup/generate_container_user

@@ -1,3 +1,20 @@
+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
+  elif [ -r /usr/lib64/libnss_wrapper.so ]; then
+      LD_PRELOAD=/usr/lib64/libnss_wrapper.so
+  else
+      echo "no libnss_wrapper.so installed!"
+      exit 1
+  fi
+}
+
 # Set current user in nss_wrapper
 USER_ID=$(id -u)
 GROUP_ID=$(id -g)
@@ -24,14 +41,7 @@ if [ x"$USER_ID" != x"0" ]; then
     export NSS_WRAPPER_PASSWD
     export NSS_WRAPPER_GROUP
 
-    if [ -r /usr/lib/libnss_wrapper.so ]; then
-        LD_PRELOAD=/usr/lib/libnss_wrapper.so
-    elif [ -r /usr/lib64/libnss_wrapper.so ]; then
-        LD_PRELOAD=/usr/lib64/libnss_wrapper.so
-    else
-        echo "no libnss_wrapper.so installed!"
-        exit 1
-    fi
+    detect_libnss_wrapper
     echo "nss_wrapper location: $LD_PRELOAD"
     export LD_PRELOAD
 fi