tests/vm: Added configuration file support

tests/vm: Added configuration file support

Changes to tests/vm/basevm.py to allow accepting a configuration file
as a parameter. Allows for specifying VM options such as
cpu, machine, memory, and arbitrary qemu arguments for specifying options
such as NUMA configuration.
Also added an example conf_example_aarch64.yml and conf_example_x86.yml.

Signed-off-by: Robert Foley <robert.foley@linaro.org>
Reviewed-by: Peter Puhov <peter.puhov@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200601211421.1277-4-robert.foley@linaro.org>
Message-Id: <20200701135652.1366-8-alex.bennee@linaro.org>