Manage criteria in TestCase

Manage criteria in TestCase

It converts all criteria values to the corresponding percent in
functest/ci/testcases.yaml.

Result is expected to be equal or greater than criteria. If both are 0,
result is considered as false.

It is compatible with the old behavior but warns to update.
It will allow a safer remove.

It also fixes a bug in test_tempest to allow merging [1] and
tier_handler.py which required that type criteria was str.

[1] https://gerrit.opnfv.org/gerrit/#/c/27949/

Change-Id: Ib6edcfa3103b7d51b0bdc83119f1cea2a8be9fbc
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>