bitbake: progress.py: Fix traceback when running goggle ui

bitbake: progress.py: Fix traceback when running goggle ui

The following traceback appears when running the following command after the
devshell is exited.

bitbake -u goggle -c devshell busybox

-- traceback --
Traceback (most recent call last):
  File "/work/bitbake/lib/bb/ui/goggle.py", line 35, in event_handle_idle_func
    build.handle_event (event, pbar)
  File "/work/bitbake/lib/bb/ui/crumbs/runningbuild.py", line 299, in handle_event
    pbar.set_text(event.msg)
AttributeError: 'ProgressBar' object has no attribute 'set_text'

(Bitbake rev: a6cc53cdb3c34fc8fd01bbc5ce0008429dc6785c)

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>