cros_build_lib: Add root user check helpers

Add helper functions, to check root privilege for the user.

BUG=b:218521368
TEST=run_tests lib/ scripts/ service/ cli/

Change-Id: Idd0ad8be3764b323b140d3e334399eef4d21e8a6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3491293
Tested-by: Ram Chandrasekar <rchandrasekar@google.com>
Auto-Submit: Ram Chandrasekar <rchandrasekar@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Ram Chandrasekar <rchandrasekar@google.com>
diff --git a/scripts/run_tests.py b/scripts/run_tests.py
index b61dc36..c9f78e0 100644
--- a/scripts/run_tests.py
+++ b/scripts/run_tests.py
@@ -31,6 +31,7 @@
 from chromite.lib import cros_build_lib
 from chromite.lib import gs
 from chromite.lib import namespaces
+from chromite.lib import osutils
 
 
 def main(argv):
@@ -84,7 +85,7 @@
 
 def re_execute_with_namespace(argv, network=False):
   """Re-execute as root so we can unshare resources."""
-  if os.geteuid() != 0:
+  if osutils.IsNonRootUser():
     cmd = [
         'sudo',
         'HOME=%s' % os.environ['HOME'],