Move enforcer convergence check into verify phase

[jonathanaustin]

Move the enforcer plugin convergence check in qa-parent into the same "verify" phase as all other QA checks. This can be done by putting the check in its own plugin execution in the verify phase.

The new execution step can also have its own skip property so it does not affect the enforcer plugin execution in bordertech_parent. This new skip property can also default to the bt.qa.skip property like the other qa skip properties.