key_value_store: pull LoadKeyValueFile into a module

This isn't used too often, so lets pull it out into a standalone
module.  It also has no real deps on other bits, so move it to
the utils namespaces.

BUG=chromium:997354
TEST=`./run_tests` passes

Change-Id: Ieee6b3476600cca98aaad7597cda57b6a79f3d55
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1790373
Reviewed-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cros_setup_toolchains.py b/scripts/cros_setup_toolchains.py
index 7262b5a..9546d18 100644
--- a/scripts/cros_setup_toolchains.py
+++ b/scripts/cros_setup_toolchains.py
@@ -22,6 +22,7 @@
 from chromite.lib import osutils
 from chromite.lib import parallel
 from chromite.lib import toolchain
+from chromite.utils import key_value_store
 
 # Needs to be after chromite imports.
 import lddtree
@@ -1071,7 +1072,7 @@
   envds = glob.glob(envd)
   assert len(envds) == 1, '%s: should have exactly 1 env.d file' % envd
   envd = envds[0]
-  return cros_build_lib.LoadKeyValueFile(envd)[var]
+  return key_value_store.LoadFile(envd)[var]
 
 
 def _ProcessBinutilsConfig(target, output_dir):