[YOCTO #2605].
Added openssh-sftp-server to the tools-debug IMAGE_FEATURE.
(From OE-Core rev: a6b6df1350149c116050cb93c3c7b4802c709d31)
Signed-off-by: Lianhao Lu <lianhao.lu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>