labs: fix HTTP_EXCEPTIONS check
labs: fix HTTP_EXCEPTIONS check

If HTTP_EXCEPTIONS is not 0, it is a string. In that case, the
comparison "-ne 0" results in an error and the script aborts.
Use string comparison instead.

Change-Id: I2e9311e6e0577b213281eaa7b0227ca51d59368d

dguitarbite/OpenStack-Labs,dguitarbite/OpenStack-Labs,openstack/training-labs,openstack/training-labs,dguitarbite/OpenStack-Labs,openstack/training-labs