bitbake: cooker: encode event objects to base64

pickle converts python objects into the binary form that can't be
decoded to text and therefore can't be converted to JSON format.

Attempt to convert event objects raises this error:
TypeError:
    b'\x80\x03cbb.runqueue\nrunQueueTaskSkipped\nq\x00)...
    is not JSON serializable

Encoded pickled event objects to base64 to be able to convert data
structure to JSON.

[YOCTO #9803]

(Bitbake rev: f18055237e6084f90f6221442e3ba021dcc59c50)

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/cooker.py

@@ -44,6 +44,7 @@ import prserv.serv
 import pyinotify
 import json
 import pickle
+import codecs
 
 logger      = logging.getLogger("BitBake")
 collectlog  = logging.getLogger("BitBake.Collection")
@@ -143,7 +144,9 @@ class EventLogWriteHandler:
         def write_event(self, event):
             with open(self.eventfile, "a") as f:
                 try:
-                    f.write("%s\n" % json.dumps({"class":event.__module__ + "." + event.__class__.__name__, "vars":json.dumps(pickle.dumps(event)) }))
+                    str_event = codecs.encode(pickle.dumps(event), 'base64').decode('utf-8')
+                    f.write("%s\n" % json.dumps({"class": event.__module__ + "." + event.__class__.__name__,
+                                                 "vars": str_event}))
                 except Exception as e:
                     import traceback
                     print(e, traceback.format_exc())