fix: improve port checks

[abuchanan-airbyte]

This PR is doing a few things related to improving the port checks (portAvailable and getPort):

• getPort checks that the container status is running and returns an error otherwise
• portAvailable is only called when installing a new cluster (no existing cluster)
• portAvailable a nicer error message by looking for "address in use" error codes.
• portAvailable doesn't try to guess whether an existing port is used by Airbyte or not (since it's now only called when no cluster exists)

Some code-level changes:

• I moved some docker mock test stuff into dockertest
• I merged docker.Port() into getPort() - it was only being called from getPort and with it merged, I can easily do the status == running check, and the tests seem improved as well.
• getPort() now takes a cluster name, instead of the whole k8s.Provider

I made these changes to address to scenarios:

1. I have another, unrelated container bound to port 8000
2. I have an abctl cluster that was created but the container has been stopped (e.g. I restarted my Docker Desktop)

These changes improved the experience in these cases:

Unrelated container bound to port 8000

Before:

After:

Cluster in stopped container

Before:

After:

[abuchanan-airbyte]

I think this broke something with the spinners

[colesnodgrass]

Should we include the keys here as well?