gitignore: Add hob-image-*.bb

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

.gitignore

@@ -9,6 +9,7 @@ sources/
 meta-*
 !meta-skeleton
 !meta-hob
+hob-image-*.bb
 *.swp
 *.orig
 *.rej