Fix deprecation warning from Jinja2 with Python3
Fix deprecation warning from Jinja2 with Python3

Escape sequences need double backslashes.

Change-Id: I01b91bbc6b09442fd5f568ad65ccc95381a1c833

Linaro/lava-server,Linaro/lava-server,Linaro/lava-server,Linaro/lava-server