sanitycheck: Add info about zephyr version to the xml reports

This commit adds posibility to save zephyr version in the xml reports.
It adds 'properties' attribute to testsuite attribute. 'properties'
can contain multiple 'property' attributes. Zephyr version is added
as such 'property'.

Signed-off-by: Maciej Perkowski <Maciej.Perkowski@nordicsemi.no>