dev-manual: Fixed order for variables in ptest section.

The IMAGE_FEATURE and DISTRO_FEATURE are exchanged.

Reported-by: Jesse Zhang <sen.zhang@windriver.com>
(From yocto-docs rev: fddc1feff5670e73d28ebfca8f73eb16f2276de9)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/dev-manual/dev-manual-common-tasks.xml

@@ -3577,8 +3577,8 @@
                     which is found in the
                     <link linkend='build-directory'>Build Directory</link>:
                     <literallayout class='monospaced'>
-     EXTRA_IMAGE_FEATURES += "ptest"
-     DISTRO_FEATURES_append = " ptest-pkgs"
+     DISTRO_FEATURES_append = " ptest"
+     EXTRA_IMAGE_FEATURES += "ptest-pkgs"
                     </literallayout>
                     Once your build is complete, the ptest files are installed
                     into the <filename>/usr/lib/&lt;package&gt;/ptest</filename>