bitbake/progress: add method to pulse the progress bar

When we're running a long operation with indeterminate duration it's useful
to use the gtk.ProgressBar's pulse method to show that something is happening
but we don't know how long it will take.

Signed-off-by: Joshua Lock <josh@linux.intel.com>

bitbake/lib/bb/ui/crumbs/progress.py

@@ -15,3 +15,7 @@ class ProgressBar(gtk.Dialog):
     def update(self, x, y):
         self.progress.set_fraction(float(x)/float(y))
         self.progress.set_text("%2d %%" % (x*100/y))
+
+    def pulse(self):
+        self.progress.set_text("Loading...")
+        self.progress.pulse()