Allow socket and address/port to be used with maxadmin

It's now possible to use both a Unix domain socket and host/port
when connecting with MaxAdmin to MaxScale.

By default MaxAdmin will attempt to use the default Unix domain
socket, but if host and/or port has been specified, then an inet
socket will be used.

maxscaled will authenticate the connection attempt differently
depending on whether a Unix domain socket is used or not. If
a Unix domain socket is used, then the Linux user id will be
used for the authorization, otherwise the 1.4.3 username/password
handshake will be performed.

adminusers has now been extended so that there is one set of
functions for local users (connecting locally over a Unix socket)
and one set of functions for remote users (connecting locally
or remotely over an Inet socket).

The local users are stored in the new .../maxscale-users and the
remote users in .../passwd. That is, the old users of a 1.4
installation will work as such in 2.0.

One difference is that there will be *no* default remote user.
That is, remote users will always have to be added manually using
a local user.

The implementation is shared; the local and remote alternatives
use common functions to which the hashtable and filename to be
used are forwarded.

The commands "[add|remove] user" behave now exactly like they did
in 1.4.3, and also all existing users work out of the box.

In addition there is now the commands "[enable|disable] account"
using which Linux accounts can be enabled for MaxAdmin usage.

server/modules/include/maxadmin.h

@@ -13,12 +13,19 @@
  * Public License.
  */
 
-#define MAXADMIN_DEFAULT_SOCKET "/tmp/maxadmin.sock"
+#define MAXADMIN_DEFAULT_SOCKET                "/tmp/maxadmin.sock"
 
 #define MAXADMIN_CONFIG_DEFAULT_SOCKET_TAG_LEN 7
-#define MAXADMIN_CONFIG_DEFAULT_SOCKET_TAG "default"
-#define MAXADMIN_GETPWUID_BUF_LEN 255
-#define MAXADMIN_AUTH_REPLY_LEN 6
-#define MAXADMIN_FAILED_AUTH_MESSAGE "FAILED"
+#define MAXADMIN_CONFIG_DEFAULT_SOCKET_TAG     "default"
+
+#define MAXADMIN_AUTH_REPLY_LEN                6
+#define MAXADMIN_AUTH_FAILED_REPLY             "FAILED"
+#define MAXADMIN_AUTH_SUCCESS_REPLY            "OK----"
+
+#define MAXADMIN_AUTH_USER_PROMPT              "USER"
+#define MAXADMIN_AUTH_USER_PROMPT_LEN          4
+
+#define MAXADMIN_AUTH_PASSWORD_PROMPT          "PASSWORD"
+#define MAXADMIN_AUTH_PASSWORD_PROMPT_LEN      8
 
 #endif

server/modules/include/maxscaled.h

@@ -28,16 +28,17 @@
 #include <spinlock.h>
 #include <housekeeper.h>
 /**
- * The telnetd specific protocol structure to put in the DCB.
+ * The maxscaled specific protocol structure to put in the DCB.
  */
-typedef struct  maxscaled
+typedef struct maxscaled
 {
-    SPINLOCK    lock;       /**< Protocol structure lock */
-    int     state;      /**< The connection state */
-    char        *username;  /**< The login name of the user */
+    SPINLOCK lock;      /**< Protocol structure lock */
+    int      state;     /**< The connection state */
+    char    *username;  /**< The login name of the user */
 } MAXSCALED;
 
-#define MAXSCALED_STATE_LOGIN   1   /**< Waiting for credentials */
-#define MAXSCALED_STATE_DATA    2   /**< User logged in */
+#define MAXSCALED_STATE_LOGIN   1   /**< Waiting for user */
+#define MAXSCALED_STATE_PASSWD  2   /**< Waiting for password */
+#define MAXSCALED_STATE_DATA    3   /**< User logged in */
 
 #endif