Fix rally-gate.sh exit status

Exit status should be set to non-zero if rally sla_check was not
successful. Bash option pipefail save any non-zero exit status
from piped commands.

Changed some default scenarios runners agrument

Remove SLA from 2 non working benchmark scenarios.
Related-Bug: #1354683

Change-Id: I327f23e460737ffe3a4fec42afcfbb387ae81bfb