buildman: Add an option to specify the buildman config file

Add a new --config-file option (-G) to specify a different configuration
file from the default ~/.buildman.

Reported-by: Tom Rini <trini@ti.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/control.py b/tools/buildman/control.py
index cc8593f..0c9e2cb 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -86,7 +86,7 @@
     """
     gitutil.Setup()
 
-    bsettings.Setup()
+    bsettings.Setup(options.config_file)
     options.git_dir = os.path.join(options.git, '.git')
 
     toolchains = toolchain.Toolchains()