ovsdb-server: Maintain the database lock with --detach.

Before this commit, "ovsdb-server --detach" would detach after it opened
the database file, which meant that the child process did not hold the
file lock on the database file (because a forked child process does not
inherit its parents' locks).  This commit fixes the problem by making
ovsdb-server open the database only after it has detached.  This fix, in
turn, required that daemonize() not chdir to /, because this would break
databases whose names are given relative to the current directory, and so
this commit also changes ovsdb-server to do so later.

lib/daemon.c

@@ -81,6 +81,13 @@ set_no_chdir(void)
     chdir_ = false;
 }
 
+/* Will we chdir to "/" as part of daemonizing? */
+bool
+is_chdir_enabled(void)
+{
+    return chdir_;
+}
+
 /* Normally, die_if_already_running() will terminate the program with a message
  * if a locked pidfile already exists.  If this function is called,
  * die_if_already_running() will merely log a warning. */
@@ -98,6 +105,13 @@ set_detach(void)
     detach = true;
 }
 
+/* Will daemonize() really detach? */
+bool
+get_detach(void)
+{
+    return detach;
+}
+
 /* If a pidfile has been configured and that pidfile already exists and is
  * locked by a running process, returns the pid of the running process.
  * Otherwise, returns 0. */