Added usher to run pwconv and grpconv if necessary

SNAP/usher

@@ -0,0 +1,34 @@
+#!/bin/bash
+
+set -e
+
+case $1 in
+  preinst)
+    exit 0
+    ;;
+  postinst)
+    if [[ ${TARGET} ]]; then
+      if [ ! -f ${TARGET}/etc/shadow ]; then
+        chroot ${TARGET} pwconv
+      fi
+
+      if [ ! -f ${TARGET}/etc/gshadow ]; then
+        chroot ${TARGET} grpconv
+      fi
+    else
+      if [ ! -f /etc/shadow ]; then
+        pwconv
+      fi
+
+      if [ ! -f /etc/gshadow ]; then
+        grpconv
+      fi
+    fi
+    ;;
+  prerm)
+    exit 0
+    ;;
+  postrm)
+    exit 0
+    ;;
+esac