oeqa/selftest: skip test_incremental_image_generation if not using rpm

We have just implemented incremental ipk image generation, but at the
moment this test doesn't support that, so skip it if not using rpm.

(From OE-Core rev: e920c1a62705524be71dc5f9e4527b396ca83dca)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/selftest/buildoptions.py

@@ -13,6 +13,9 @@ class ImageOptionsTests(oeSelfTest):
 
     @testcase(761)
     def test_incremental_image_generation(self):
+        image_pkgtype = get_bb_var("IMAGE_PKGTYPE")
+        if image_pkgtype != 'rpm':
+            self.skipTest('Not using RPM as main package format')
         bitbake("-c cleanall core-image-minimal")
         self.write_config('INC_RPM_IMAGE_GEN = "1"')
         self.append_config('IMAGE_FEATURES += "ssh-server-openssh"')