mysql: Handle case where .mysql.hash doesn't exist

mysql/debian/postinst

@@ -45,9 +45,12 @@ fi
 # Add an admin user with user/password authentication for phpmyadmin if one doesn't already exist
 #
 if grep -qx 'password = ' /etc/mysql/debian.cnf && [ "$(mysql -u root -se "select exists(select user from mysql.user where user = 'admin');")" = "0" ] ; then
+  echo "I: Adding 'admin'@'localhost' MySQL user"
   if [ -e /etc/first-boot.d/.mysql.hash ]; then
-    echo "I: Adding 'admin'@'localhost' MySQL user"
     mysql -u root -e "grant all privileges on *.* to 'admin'@'localhost' identified by password '*$(cat /etc/first-boot.d/.mysql.hash)' with grant option;"
+  else
+    read -p "Enter password for admin@localhost MySQL user: " password
+    mysql -u root -e "grant all privileges on *.* to 'admin'@'localhost' identified by '$password' with grant option;"
   fi
 fi