mender: Use += rather than _append for IMAGE_FSTYPES.

Using _append breaks initramfs builds and attempts to build Mender style
images for them.  Basically, the initramfs image files set a new value
of IMAGE_FSTYPES but when we use _append we are applied _after_ that;
using += makes sure that the override done in the image recipe takes
place.

More details can be seen in this discussion:
    Linaro/meta-qcom#61

Changelog: Title
Signed-off-by: Drew Moseley <drew.moseley@northern.tech>

meta-mender-core/classes/mender-part-images.bbclass

@@ -282,7 +282,7 @@ python() {
 
     d.setVar('LIVE_ROOTFS_TYPE', type)
     d.setVar('ROOTFS', "${IMGDEPLOYDIR}/${IMAGE_LINK_NAME}.%s.bz2" % type)
-    d.setVar('IMAGE_FSTYPES_append', ' %s.bz2 ' % type)
+    d.appendVar('IMAGE_FSTYPES', ' %s.bz2 ' % type)
 
     # Remove the boot option on the Live installer; it won't work since Mender hard codes
     # the device nodes

meta-mender-core/classes/mender-setup-image.inc

@@ -1,9 +1,9 @@
-IMAGE_FSTYPES_append = "${@bb.utils.contains('DISTRO_FEATURES', 'mender-image', ' mender mender.bmap', '', d)}"
-IMAGE_FSTYPES_append = "${@bb.utils.contains('DISTRO_FEATURES', 'mender-image-sd', ' sdimg sdimg.bmap', '', d)}"
-IMAGE_FSTYPES_append = "${@bb.utils.contains('DISTRO_FEATURES', 'mender-image-ubi', ' ubimg mtdimg ubimg.bmap', '', d)}"
-IMAGE_FSTYPES_append = "${@bb.utils.contains('DISTRO_FEATURES', 'mender-image-uefi', ' uefiimg uefiimg.bmap', '', d)}"
-IMAGE_FSTYPES_append = "${@bb.utils.contains('DISTRO_FEATURES', 'mender-image-bios', ' biosimg biosimg.bmap', '', d)}"
-IMAGE_FSTYPES_append = "${@bb.utils.contains('DISTRO_FEATURES', 'mender-image-gpt', ' gptimg gptimg.bmap', '', d)}"
+IMAGE_FSTYPES += "${@bb.utils.contains('DISTRO_FEATURES', 'mender-image', ' mender mender.bmap', '', d)}"
+IMAGE_FSTYPES += "${@bb.utils.contains('DISTRO_FEATURES', 'mender-image-sd', ' sdimg sdimg.bmap', '', d)}"
+IMAGE_FSTYPES += "${@bb.utils.contains('DISTRO_FEATURES', 'mender-image-ubi', ' ubimg mtdimg ubimg.bmap', '', d)}"
+IMAGE_FSTYPES += "${@bb.utils.contains('DISTRO_FEATURES', 'mender-image-uefi', ' uefiimg uefiimg.bmap', '', d)}"
+IMAGE_FSTYPES += "${@bb.utils.contains('DISTRO_FEATURES', 'mender-image-bios', ' biosimg biosimg.bmap', '', d)}"
+IMAGE_FSTYPES += "${@bb.utils.contains('DISTRO_FEATURES', 'mender-image-gpt', ' gptimg gptimg.bmap', '', d)}"
 
 MACHINE_ESSENTIAL_EXTRA_RDEPENDS_append_mender-image_x86 =     " kernel-image"
 MACHINE_ESSENTIAL_EXTRA_RDEPENDS_append_mender-image_x86-64 =  " kernel-image"

tests/acceptance/test_build.py

@@ -132,7 +132,7 @@ def test_tenant_token(self, prepared_test_build):
         add_to_local_conf(prepared_test_build, 'MENDER_TENANT_TOKEN = "%s"'
                           %  "authtentoken")
 
-        add_to_local_conf(prepared_test_build, 'IMAGE_FSTYPES_append = " dataimg"')
+        add_to_local_conf(prepared_test_build, 'IMAGE_FSTYPES += "dataimg"')
 
         run_bitbake(prepared_test_build)