In order to know we are running under a zuul slave,
we need to add an environment variable. In this case
it is ZUUL=true. This will allow the kata-containers
scripts to run the tests with the appropiate flags.
Change-Id: Ib040c032ad49beb5e2041e92efe41ce4e8b98799
Signed-off-by: Salvador Fuentes <salvador.fuentes@intel.com>