bitbake: lib: implement basic task progress support

For long-running tasks where we have some output from the task that
gives us some idea of the progress of the task (such as a percentage
complete), provide the means to scrape the output for that progress
information and show it to the user in the default knotty terminal
output in the form of a progress bar. This is implemented using a new
TaskProgress event as well as some code we can insert to do output
scanning/filtering.

Any task can fire TaskProgress events; however, if you have a shell task
whose output you wish to scan for progress information, you just need to
set the "progress" varflag on the task. This can be set to:
 * "percent" to just look for a number followed by a % sign
 * "percent:<regex>" to specify your own regex matching a percentage
   value (must have a single group which matches the percentage number)
 * "outof:<regex>" to look for the specified regex matching x out of y
   items completed (must have two groups - first group needs to be x,
   second y).
We can potentially extend this in future but this should be a good
start.

Part of the implementation for [YOCTO #5383].

(Bitbake rev: 0d275fc5b6531957a6189069b04074065bb718a0)

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

bitbake/lib/progressbar/progressbar.py

@@ -3,6 +3,8 @@
 # progressbar  - Text progress bar library for Python.
 # Copyright (c) 2005 Nilton Volpato
 #
+# (With some small changes after importing into BitBake)
+#
 # This library is free software; you can redistribute it and/or
 # modify it under the terms of the GNU Lesser General Public
 # License as published by the Free Software Foundation; either
@@ -261,12 +263,14 @@ class ProgressBar(object):
         now = time.time()
         self.seconds_elapsed = now - self.start_time
         self.next_update = self.currval + self.update_interval
-        self.fd.write(self._format_line() + '\r')
+        output = self._format_line()
+        self.fd.write(output + '\r')
         self.fd.flush()
         self.last_update_time = now
+        return output
 
 
-    def start(self):
+    def start(self, update=True):
         """Starts measuring time, and prints the bar at 0%.
 
         It returns self so you can use it like this:
@@ -289,8 +293,12 @@ class ProgressBar(object):
             self.update_interval = self.maxval / self.num_intervals
 
 
-        self.start_time = self.last_update_time = time.time()
-        self.update(0)
+        self.start_time = time.time()
+        if update:
+            self.last_update_time = self.start_time
+            self.update(0)
+        else:
+            self.last_update_time = 0
 
         return self