Active channels mapping should not delete last active channel

[colin-axner]

Summary

Following #700 we won't be capable of checking the connection sequences against the newly created channel since the active channel mapping is deleted upon channel closure.

Problem Definition

The connection sequences used for verifying that the new channel is created on the right connections is moved from the portID to the channel structure, but the channel ID of the old channel is removed from state upon channel closure

Proposal

Do not delete the channel ID upon channel closure. GetActiveChannel should check if the active channel is in OPEN state. If the channel is in CLOSED state, a new channel may be created to become the new active channel. This allows the connection sequence and other information in Metadata to be checked upon activating a new channel for a closed channel. The existing API may be modified to cleanly implement this new functionality.

---

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged/assigned