sstatesig.py: make it fatal error when sstate manifest isn't found

* all known issues in this area were fixed, make it fatal that it
  cannot be overlooked if someone triggers this issue again

(From OE-Core rev: 64b89f3c8fc31842256c482a3039d90d3f12c1cc)

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oe/sstatesig.py

@@ -453,7 +453,7 @@ def find_sstate_manifest(taskdata, taskdata2, taskname, d, multilibcache):
         manifest = d2.expand("${SSTATE_MANIFESTS}/manifest-%s-%s.%s" % (pkgarch, taskdata, taskname))
         if os.path.exists(manifest):
             return manifest, d2
-    bb.error("Manifest %s not found in %s (variant '%s')?" % (manifest, d2.expand(" ".join(pkgarchs)), variant))
+    bb.fatal("Manifest %s not found in %s (variant '%s')?" % (manifest, d2.expand(" ".join(pkgarchs)), variant))
     return None, d2
 
 def OEOuthashBasic(path, sigfile, task, d):