'st2cd' shouldn't set any version variables in K/V

[arm4b]

Example: during the release machinery we set st2_stable_version in K/V and rely on it.

With the new st2cicd server, which could be re-provisioned anytime by us, this becomes a problem to update ops-infra Ansible repo with the new K/V value (infra-as-a-code 👊 ).
Example: https://github.com/StackStorm/ops-infra/pull/186 👎

The solution is to commit the version used directly to st2cd repo itself instead of K/V, same as we do via automation:
2c19af5