In cockroachdb#98076, we started validating hostnames before running any commands
to avoid situations where a stale cache could lead to unintended
interference with other clusters due to public IP reuse. The check
relies on the VM's `hostname` matching the expected cluster name in
the cache. GCP and Azure clusters set the hostname to the instance
name by default, but that is not the case for AWS; the aforementioned
PR explicitly sets the hostname when the instance is created.

However, in the case of long running AWS clusters (created before host
validation was introduced) or clusters that are created with an
outdated version of `roachprod`, the hostname will still be the
default AWS hostname, and any interaction with that cluster will fail
if using a recent `roachprod` version. To remedy this situation, this
commit includes:

* better error reporting. When we attempt to run a command on an AWS
cluster and host validation fails, we display a message to the user
explaining that their hostnames may need fixing.

* if the user confirms that the cluster still exists (by running
`roachprod list`), they are able to automatically fix the hostnames to
the expected value by running a new `fix-long-running-aws-hostnames`
command. This is a temporary workaround that should be removed once we
no longer have clusters that would be affected by this issue.

This commit will be reverted once we no longer have clusters created
with the default hostnames; this will be easier to achieve once we
have an easy way for everyone to upgrade their `roachprod` (see cockroachdb#97311).

Epic: none

Release note: None