(MODULES-7857) Support user creation on galera. Add IF NOT EXISTS to CREATE USER in mysql_user provider

Author: Maksim Fedotov

lib/puppet/provider/mysql_user/mysql.rb

@@ -61,16 +61,21 @@ def create
 
     # Use CREATE USER to be compatible with NO_AUTO_CREATE_USER sql_mode
     # This is also required if you want to specify a authentication plugin
+    if_not_exists = if newer_than('mysql' => '5.7', 'percona' => '5.7', 'mariadb' => '10.1.3')
+                      'IF NOT EXISTS '
+                    else
+                      ''
+                    end
     if !plugin.nil?
       if plugin == 'sha256_password' && !password_hash.nil?
-        self.class.mysql_caller("CREATE USER '#{merged_name}' IDENTIFIED WITH '#{plugin}' AS '#{password_hash}'", 'system')
+        self.class.mysql_caller("CREATE USER #{if_not_exists}'#{merged_name}' IDENTIFIED WITH '#{plugin}' AS '#{password_hash}'", 'system')
       else
-        self.class.mysql_caller("CREATE USER '#{merged_name}' IDENTIFIED WITH '#{plugin}'", 'system')
+        self.class.mysql_caller("CREATE USER #{if_not_exists}'#{merged_name}' IDENTIFIED WITH '#{plugin}'", 'system')
       end
       @property_hash[:ensure] = :present
       @property_hash[:plugin] = plugin
     else
-      self.class.mysql_caller("CREATE USER '#{merged_name}' IDENTIFIED BY PASSWORD '#{password_hash}'", 'system')
+      self.class.mysql_caller("CREATE USER #{if_not_exists}'#{merged_name}' IDENTIFIED BY PASSWORD '#{password_hash}'", 'system')
       @property_hash[:ensure] = :present
       @property_hash[:password_hash] = password_hash
     end