Update stage1 and stage3 to run robot tests with tag

This commit updates stage1 and stage3 to allow running robot
tests in stage3 by default for every commit.

The commit removes param DO_STAGE_4 since it is confusing. Only
params DO_ROBOT and ROBOT_TAG will be used. If DO_ROBOT is set
to true, robot tests will be run in stage3 for all tests containing
the tag indicated by ROBOT_TAG. The param ROBOT_TAG replaces
the previous param TEST_NAME.

MDG stage1 can specify params DO_ROBOT and ROBOT_TAG. If specified,
they will be used. Otherwise, the default for stage3 will apply
(DO_ROBOT=true, ROBOT_TAG=sanity).

Daily job, which will run stage1, can also specify params DO_ROBOT
and ROBOT_TAG. In principle, they will be set as follows:
DO_ROBOT=true, ROBOT_TAG=daily.

Stage1 job, in case of failure, will send an e-mail to OSM_MDL
mailing list reporting the failure. The mail will only be sent
if the name of the job starts with "daily-stage_4".

Change-Id: If481f2da01f4c811495504329fe7b6d7bd88c9de
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>