Fixup render-template to look for .jinja2 files.
Fixup render-template to look for .jinja2 files.

Add a note on how to use the system paths and where to put
the test files.

Change-Id: I6b8c7984b3c85ba96fb305edb742700f14fe791a

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