shared/log: read /proc/cmdline only in daemons

http://lists.freedesktop.org/archives/systemd-devel/2015-February/027960.html
(cherry picked from commit ee46e55570)

Conflicts:
	src/shared/log.c

src/shared/log.c

@@ -910,7 +910,11 @@ static int parse_proc_cmdline_item(const char *key, const char *value) {
 void log_parse_environment(void) {
         const char *e;
 
-        parse_proc_cmdline(parse_proc_cmdline_item);
+        if (get_ctty_devnr(0, NULL) < 0)
+                /* Only try to read the command line in daemons.
+                   We assume that anything that has a controlling
+                   tty is user stuff. */
+                (void) parse_proc_cmdline(parse_proc_cmdline_item);
 
         e = secure_getenv("SYSTEMD_LOG_TARGET");
         if (e && log_set_target_from_string(e) < 0)