Logging target must be explicitly defined.

Whether the log-file should be written to the filesystem or to
shared memory must now be explicitly defined when calling
skygw_logmanager_init() (instead of passing that via the argc/argv
construct).

Also, the meaning of '-l' when invoking maxscale has been changed.

Earlier -l [file|shm] specified whether the trace and debug logs
should be written to shared memory (while the error and message
logs always were written to the filesystem) and the _default_
was to write them to shared memory.

Now, with only one file, '-l' has still the same meaning, but it
decides whether the one and only logfile should be written to shared
memory, or the filesystem and the _default_ is to write it to the
filesystem.

log_manager/log_manager.h

@@ -42,7 +42,6 @@ typedef enum
     LOGFILE_LAST = LOGFILE_DEBUG
 } logfile_id_t;
 
-
 typedef enum
 {
     FILEWRITER_INIT,
@@ -50,6 +49,13 @@ typedef enum
     FILEWRITER_DONE
 } filewriter_state_t;
 
+typedef enum
+{
+    LOG_TARGET_DEFAULT = 0,
+    LOG_TARGET_FS      = 1, // File system
+    LOG_TARGET_SHMEM   = 2, // Shared memory
+} log_target_t;
+
 /**
 * Thread-specific logging information.
 */
@@ -145,7 +151,7 @@ int mxs_log_rotate();
 int mxs_log_enable_priority(int priority);
 int mxs_log_disable_priority(int priority);
 
-bool skygw_logmanager_init(const char* logdir, int argc, char* argv[]);
+bool skygw_logmanager_init(const char* logdir, log_target_t target, int argc, char* argv[]);
 void skygw_logmanager_done(void);
 void skygw_logmanager_exit(void);