openocd.c: call server_quit() for cmd line with -c shutdown

openocd.c: call server_quit() for cmd line with -c shutdown

If OpenOCD command line contains -c shutdown, server_quit() is not called.
Though if -c init is also on command line, gdb_server is already initialized.

Call server_quit() on both successful and failure exit from command line.

Change-Id: I6df41c5df045b61d84a5515d1abaa5dc96bc30ac
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/4409
Tested-by: jenkins