bitbake: lib/bb/siggen.py: insert a colon between class and recipe name

before:
  virtual:nativeautomake_1.12.1.bb.do_compile
after:
  virtual:native:automake_1.12.1.bb.do_compile

This separation ensures that the key is readable, and if necessary,
parsable.

Unfortunately this invalidates previous native sstate signatures with
OE-Core - not much that can be done about that; however that occurs
frequently during the development cycle so it's par for the course.

(Bitbake rev: 5b96c32dad256090e9bda5af0f80c7dbcc90bde8)

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

bitbake/lib/bb/siggen.py

@@ -290,7 +290,7 @@ def dump_this_task(outfile, d):
 
 def clean_basepath(a):
     if a.startswith("virtual:"):
-        b = a.rsplit(":", 1)[0] + a.rsplit("/", 1)[1]
+        b = a.rsplit(":", 1)[0] + ":" + a.rsplit("/", 1)[1]
     else:
         b = a.rsplit("/", 1)[1]
     return b