Get GDBserver pid on remote target

Hi,
We see the following fail in the real remote testing...

(gdb) Executing on target: kill -9 29808    (timeout = 300)
spawn [open ...]^M
sh: 1: kill: No such process

The test tries to kill gdbserver in this way:

set server_pid [exp_pid -i [board_info target fileid]]
remote_exec target "kill -9 $server_pid"

in native testing, we'll get the pid of spawned gdbserver, however, in
remote testing, we'll get the pid of ssh session, since we start
gdbserver on the remote target through ssh.  The pid on build doesn't
exist on target.

In this patch, we tweak server-kill.c to get the parent pid, which is
the pid of GDBserver.  GDB gets it and kill GDBserver on target.

gdb/testsuite:

2014-10-11  Yao Qi  <yao@codesourcery.com>

	* gdb.server/server-kill.c: Include sys/types.h and unistd.h.
	(main): Call getppid.
	* gdb.server/server-kill.exp: Set breakpoint on line "i = 0;"
	and continue to it.  Read variable "server_pid".