oeqa/sstatetests: Ensure we cover deb packaging backend for sstate test

Currently we weren't testing the deb backaned for sstate correctness and there was a bug that had crept in. Ensure we cover all package backends with the test regardless of what the distro/conf sets.

index 07212ac..a353f67 100644
@@ -237,6 +237,7 @@ TMPDIR = "${TOPDIR}/tmp-sstatesamehash"

 BUILD_ARCH = "x86_64"
 BUILD_OS = "linux"
 SDKMACHINE = "x86_64"
+PACKAGE_CLASSES = "package_rpm package_ipk package_deb" """)
         self.track_for_cleanup(topdir + "/tmp-sstatesamehash") bitbake("core-image-sato -S none")
@@ -246,6 +247,7 @@ TMPDIR = "${TOPDIR}/tmp-sstatesamehash2" BUILD_ARCH = "i686"
 BUILD_OS = "linux"
 SDKMACHINE = "i686"
+PACKAGE_CLASSES = "package_rpm package_ipk package_deb" """)
         self.track_for_cleanup(topdir + "/tmp-sstatesamehash2") bitbake("core-image-sato -S none")