oxenstored: honour XEN_LOG_DIR defined by configure

We generate a corresponding constant (in lower case) in paths.ml. Use
that in source code to get rid of hard-coded path.

Note that with this patch the default location for xenstored*.log is
changed from /var/log to /var/log/xen.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: David Scott <dave@recoil.org>

tools/ocaml/xenstored/logging.ml

@@ -154,7 +154,7 @@ let make_syslog_logger facility =
 		Syslog.log facility level s in
 	{ stop = nothing; restart = nothing; rotate = nothing; write=write }
 
-let xenstored_log_destination = ref (File "/var/log/xenstored.log")
+let xenstored_log_destination = ref (File (Paths.xen_log_dir ^ "/xenstored.log"))
 let xenstored_log_level = ref Warn
 let xenstored_log_nb_files = ref 10
 let xenstored_log_nb_lines = ref 13215
@@ -262,7 +262,7 @@ let sanitize_data data =
 	String.escaped data
 
 let activate_access_log = ref true
-let access_log_destination = ref (File "/var/log/xenstored-access.log")
+let access_log_destination = ref (File (Paths.xen_log_dir ^ "/xenstored-access.log"))
 let access_log_nb_files = ref 20
 let access_log_nb_lines = ref 13215
 let access_log_nb_chars = ref 180