bitbake: bb.event: fix infinite loop on print_ui_queue

If bitbake ends before _uiready and bb.event.LogHandler was add
to the bitbake logger it causes an infinite loop when logging
something.

The scenario is print_ui_queue is called at exit and executes
the log handlers [2] one of them is bb.event.LogHandler this handler
appends the same entry to ui_queue causing the inifine loop [3].

In order to fix a new copy of the ui_queue list is created when iterate
ui_queue.

[YOCTO #10399]

[1] https://bugzilla.yoctoproject.org/show_bug.cgi?id=10399#c0
[2] http://git.openembedded.org/bitbake/tree/lib/bb/event.py?id=41d9cd41d40b04746c82b4a940dca47df02514fc#n156
[3]
http://git.openembedded.org/bitbake/tree/lib/bb/event.py?id=41d9cd41d40b04746c82b4a940dca47df02514fc#n164

(Bitbake rev: 46fecca9d531a07788b5cac8b2dc6a8267d8b6d0)

Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/event.py

@@ -139,7 +139,7 @@ def print_ui_queue():
 
         # First check to see if we have any proper messages
         msgprint = False
-        for event in ui_queue:
+        for event in ui_queue[:]:
             if isinstance(event, logging.LogRecord):
                 if event.levelno > logging.DEBUG:
                     if event.levelno >= logging.WARNING:
@@ -153,7 +153,7 @@ def print_ui_queue():
 
         # Nope, so just print all of the messages we have (including debug messages)
         logger.addHandler(stdout)
-        for event in ui_queue:
+        for event in ui_queue[:]:
             if isinstance(event, logging.LogRecord):
                 logger.handle(event)