lib: move a bunch of libraries to lib/

As part of the goal of making chromite/lib a general purpose set of
libraries without unneeded random dependencies, we want to make lib/
more hermetic. The ultimate goal is that lib/ modules can only depend on
other lib/ modules or on third-party packages (that are provided either
by a virtualenv or by whoever choses to use lib/ libs, but are not
vendored in chromite itself).

This is a first step in that direction, getting rid of some of the most
common lib/ -> cbuildbot/ dependency.

Since cbuildbot/constants.py is referenced from some other repositories
still, leave a symlink there that points to lib/constants.py

Also, move a few unit tests of config_lib that depended on
chromeos_config.py into chromeos_config_unittest.

BUG=chromium:645611
TEST=Unit tests pass

Change-Id: Ife55d26bffb204474a63d94b751b68a8b12c7ddd
Reviewed-on: https://chromium-review.googlesource.com/392489
Commit-Ready: Aviv Keshet <akeshet@chromium.org>
Tested-by: Aviv Keshet <akeshet@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
diff --git a/scripts/cros_generate_sysroot_unittest.py b/scripts/cros_generate_sysroot_unittest.py
index fcb5e30..3bf8184 100644
--- a/scripts/cros_generate_sysroot_unittest.py
+++ b/scripts/cros_generate_sysroot_unittest.py
@@ -9,7 +9,7 @@
 import mock
 import os
 
-from chromite.cbuildbot import constants
+from chromite.lib import constants
 from chromite.lib import cros_build_lib
 from chromite.lib import cros_test_lib
 from chromite.scripts import cros_generate_sysroot as cros_gen