container: Ensure kernbench does not use network

Previously, kernbench would always try to download a tarball of the linux source code from the internet. This wastes execution time and means that the test requires a network connection in order to run.

Let's pre-download the default version of the source code into the container image (at /fastpath/downloads) and use that instead. This solves the common case of using the default version. If a non-default version is requested, we fallback to downloading it.

While we are at it, let's delete the contents of /fastpath/mmtests/work which adds up to ~1.5G. This is not needed and was a waste of space in the container image.

Finally, update the mmtests tag to v.1.1 since we are reving the container image here.

Signed-off-by: Ryan Roberts ryan.roberts@arm.com