tests: Add sleep and debug to the jenkins presubmit.sh
tests: Add sleep and debug to the jenkins presubmit.sh

This is patch is in regard to issues discussed here:
https://www.mail-archive.com/gem5-dev@gem5.org/msg39122.html
The aim of this patch is to set a potential fix, and to give more
valuable debugging information.

It is not known why Kokoro sometimes fails, but it may be due to the
Docker service not starting fully prior to execution of the tests
within a Docker container. As such a 2 second sleep has been added
between starting the Docker service and running the tests.

The pulling of the docker images has been separated out to run at the
start of testing. This should help us determine whether the issue lays
with the pulling of an image or the running of a container.

The bash debug flag `-x` has been set so the expansion of each line can
be determined upon the event of a failure.

This patch will be reverted if it is found to not solve the issue.

Change-Id: I0d2dd8a080f64296e55f4b6de9a036d94d19c8ac
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/45999
Reviewed-by: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>
Maintainer: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5