buildman: Add helper functions for updating .config files

At present the only straightforward way to write tests that need a
slightly different configuration is to create a new board with its own
configuration. This is cumbersome.

It would be useful if buildman could adjust the configuration of a build
on the fly. In preparation for this, add a utility library which can
modify a .config file according to various parameters passed to it.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/buildman/func_test.py

@@ -182,11 +182,11 @@ class TestFunctional(unittest.TestCase):
         self._buildman_pathname = sys.argv[0]
         self._buildman_dir = os.path.dirname(os.path.realpath(sys.argv[0]))
         command.test_result = self._HandleCommand
+        bsettings.Setup(None)
+        bsettings.AddFile(settings_data)
         self.setupToolchains()
         self._toolchains.Add('arm-gcc', test=False)
         self._toolchains.Add('powerpc-gcc', test=False)
-        bsettings.Setup(None)
-        bsettings.AddFile(settings_data)
         self._boards = board.Boards()
         for brd in boards:
             self._boards.AddBoard(board.Board(*brd))