gdb.threads/multi-create-ns-info-thr.exp and native-extended-remote board

gdb.threads/multi-create-ns-info-thr.exp and native-extended-remote board

The buildbot shows that the new
gdb.threads/multi-create-ns-info-thr.exp test is timing out when
tested with --target=native-extended-remote.  The reason is:

 No breakpoints or watchpoints.
 (gdb) break main
 Breakpoint 1 at 0x10000b00: file ../../../binutils-gdb/gdb/testsuite/gdb.threads/multi-create.c, line 72.
 (gdb) run
 Starting program: /home/gdb-buildbot/fedora-21-ppc64be-1/fedora-ppc64be-native-extended-gdbserver/build/gdb/testsuite/outputs/gdb.threads/multi-create-ns-info-thr/multi-cre
 ate-ns-info-thr
 Process /home/gdb-buildbot/fedora-21-ppc64be-1/fedora-ppc64be-native-extended-gdbserver/build/gdb/testsuite/outputs/gdb.threads/multi-create-ns-info-thr/multi-create-ns-inf
 o-thr created; pid = 16266
 Unexpected vCont reply in non-stop mode: T0501:00003fffffffd190;40:00000080560fe290;thread:p3f8a.3f8a;core:0;
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 (gdb) break multi-create.c:45
 Breakpoint 2 at 0x10000994: file ../../../binutils-gdb/gdb/testsuite/gdb.threads/multi-create.c, line 45.
 (gdb) commands
 Type commands for breakpoint(s) 2, one per line.

Non-stop tests don't really work with the
--target_board=native-extended-remote board, because tests toggle
non-stop on after GDB is already connected to gdbserver, while
Currently, non-stop must be enabled before connecting.

This adjusts the test to bail if running to main fails, like all other
non-stop tests.

Note non-stop tests do work with --target_board=native-gdbserver.

gdb/testsuite/ChangeLog:
2015-02-21  Pedro Alves  <palves@redhat.com>

	* gdb.threads/multi-create-ns-info-thr.exp: Return early if
	runto_main fails.