tests: Add "mender-convert" to distro_features.

Makes it easier to detect that we are doing a mender-convert test
round.

Changelog: None

Signed-off-by: Kristian Amlie <kristian.amlie@northern.tech>

mender-convert-package

@@ -283,6 +283,7 @@ else
   # This is the name of the DISTRO_FEATURES in Yocto
   distro_feature="mender-uboot"
 fi
+distro_feature="${distro_feature} mender-convert"
 
 cat <<- EOF > deploy/${image_name}.cfg
 MENDER_BOOT_PART="${MENDER_STORAGE_DEVICE}${MENDER_BOOT_PART_INDEX}"