Sanitize language settings

To avoid commands bailing out with "unsupported locale setting" errors.

Change-Id: I54ae4cd84a0a4b4875533181b1d96563a1604775
diff --git a/stack.sh b/stack.sh
index 7da41a9..c525144 100755
--- a/stack.sh
+++ b/stack.sh
@@ -23,6 +23,13 @@
 # Make sure custom grep options don't get in the way
 unset GREP_OPTIONS
 
+# Sanitize language settings to avoid commands bailing out
+# with "unsupported locale setting" errors.
+unset LANG
+unset LANGUAGE
+LC_ALL=C
+export LC_ALL
+
 # Keep track of the devstack directory
 TOP_DIR=$(cd $(dirname "$0") && pwd)