MXS-1354: Allow creation of basic users

The type of the user being created is defined at creation time. This
allows the creation of basic users.

Although the users can be created internally, they cannot yet be created
via maxadmin or the REST API.

include/maxscale/users.h

@@ -25,6 +25,13 @@
 
 MXS_BEGIN_DECLS
 
+/** User account types */
+enum account_type
+{
+    ACCOUNT_BASIC, /**< Allows read-only access */
+    ACCOUNT_ADMIN  /**< Allows complete access */
+};
+
 /**
  * An opaque users object
  */
@@ -52,10 +59,11 @@ void users_free(USERS* users);
  * @param users    The users table
  * @param user     The user name
  * @param password The password for the user
+ * @param type     The type of account to create
  *
  * @return True if user was added
  */
-bool users_add(USERS *users, const char *user, const char *password);
+bool users_add(USERS *users, const char *user, const char *password, enum account_type type);
 
 /**
  * Delete a user from the user table.