sb: Monitor the build disk usage. Report the usage, total and various sizes

- Track the size of a build of a package in a build set to determine the
  maximum amout of disk space used. This can be used as a guide to
  documenting how much space a user needs to set aside to build a specific
  set of tools.

- The `%clean` stage of a build is now split into a separate script.
  I do not think this is an issue because I could not find any `%clean`
  sections in any build configs we have. In time support for the
  `%clean` section will be removed, the package builder cleans up.

Closes #3516

source-builder/sb/config.py

@@ -1,6 +1,6 @@
 #
 # RTEMS Tools Project (http://www.rtems.org/)
-# Copyright 2010-2016 Chris Johns (chrisj@rtems.org)
+# Copyright 2010-2018 Chris Johns (chrisj@rtems.org)
 # All rights reserved.
 #
 # This file is part of the RTEMS Tools package in 'rtems-tools'.
@@ -73,6 +73,7 @@ class package:
         self.config = config
         self.directives = {}
         self.infos = {}
+        self.sizes = {}
 
     def __str__(self):
 
@@ -218,6 +219,16 @@ class package:
     def disabled(self):
         return len(self.name()) == 0
 
+    def set_size(self, what, path_):
+        if what not in self.sizes:
+            self.sizes[what] = 0
+        self.sizes[what] += path.get_size(path_)
+
+    def get_size(self, what):
+        if what in self.sizes:
+            return self.sizes[what]
+        return 0
+
 class file:
     """Parse a config file."""