custom: split config for Custom AMI off

Up until now we have been repurposing the
Linux mbedtls AMI for use as "Custom AMI" to
run generic jobs that aren't necessarily
related to mbedtls.

This has led to some versioning problems as it's
not clear which version of an AMI is serving which
role.

Let's just split the custom AMI config off into its
own template so we can easily manage all these images
through this repo.

Signed-off-by: Kelley Spoon <kelley.spoon@linaro.org>
Change-Id: I582c1f8641d8bbe56e50714749395a615932c2e2
3 files changed