kfail two tests in no-unwaited-for-left.exp for remote target

kfail two tests in no-unwaited-for-left.exp for remote target

I see these two fails in no-unwaited-for-left.exp in remote testing
for aarch64-linux target.

...
continue
Continuing.
warning: Remote failure reply: E.No unwaited-for children left.

[Thread 1084] #2 stopped.
(gdb) FAIL: gdb.threads/no-unwaited-for-left.exp: continue stops when thread 2 exits

....
continue
Continuing.
warning: Remote failure reply: E.No unwaited-for children left.

[Thread 1081] #1 stopped.
(gdb) FAIL: gdb.threads/no-unwaited-for-left.exp: continue stops when the main thread exits

I checked the gdb.log on buildbot, and find that these two fails also
appear on Debian-i686-native-extended-gdbserver and Fedora-ppc64be-native-gdbserver-m64.
I recall that they are about local/remote parity, and related RSP is missing.
There has been already a PR 14618 about it.  This patch is to kfail them
on remote target.

gdb/testsuite:

2015-04-02  Yao Qi  <yao.qi@linaro.org>

	* gdb.threads/no-unwaited-for-left.exp: Set up kfail if target
	is remote.