Enable qTStatus packet in case it is disabled

Enable qTStatus packet in case it is disabled

Nowadays, we are using command "tstatus" to send a packet to GDBserver
in order to check the connection.  However, on the target doesn't
support tracepoint, the following error is emitted before sending any
packet to GDBserver.

tstatus^M
Trace can not be run on this target.^M
(gdb) FAIL: gdb.server/server-kill.exp: tstatus

qTStatus is disabled after receiving the empty reply during connecting
to the remote target.  When the test executes command "tstatus" again,
remote_get_trace_status returns -1 at the very beginning, and no RSP
packet is sent out.

This patch is to enable qTStatus packet again.

gdb/testsuite:

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

	* gdb.server/server-kill.exp: Execute command
	"set remote trace-status-packet on" before "tstatus".