common: create a Component class to factor out builds

Not yet finished factoring, but half way there, do for all build-

build-crosstool-ng

@@ -2,7 +2,6 @@
 
 import multiprocessing
 import os
-import shutil
 import sys
 import time
 
@@ -43,7 +42,7 @@ def main(args, extra_args=None):
     ) == 0
 
     # Build the toolchain.
-    shutil.copy2(
+    common.cp(
         os.path.join(common.root_dir, 'crosstool_ng_config', args.arch),
         defconfig_dest
     )