GetBuildMetadata: Port get_models & run_cros_config_host from cbuildbot.

BUG=chromium:1071620
TEST=manual, run_tests

Change-Id: Idc0b2578c166c16cbcf2e14c902a157ed1ddc5f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2212674
Commit-Queue: Michael Mortensen <mmortensen@google.com>
Tested-by: Michael Mortensen <mmortensen@google.com>
Reviewed-by: Alex Klein <saklein@chromium.org>
diff --git a/lib/build_target_lib.py b/lib/build_target_lib.py
index c6bb6af..d6bee95 100644
--- a/lib/build_target_lib.py
+++ b/lib/build_target_lib.py
@@ -59,6 +59,10 @@
   def name(self):
     return self._name
 
+  def full_path(self, *args):
+    """Turn a sysroot-relative path into an absolute path."""
+    return os.path.join(self.root, *[part.lstrip(os.sep) for part in args])
+
   def get_command(self, base_command):
     """Get the build target's variant of the given base command.