Generic handling of server region errors

[dadgar]

Does not early exit of errors and instead collects all and displays a warning message:

nomad server members
Name            Address         Port  Status  Leader  Protocol  Build      Datacenter  Region
server2.foo     192.168.18.171  5658  alive   false   2         0.8.0-dev  dc1         foo
server1.global  192.168.18.171  4648  alive   true    2         0.8.0-dev  dc1         global

Error determining leaders: 1 error(s) occurred:

* Region "foo": Unexpected response code: 500 (rpc error: failed to get conn: dial tcp 192.168.18.171:5657: connect: connection refused)

[github-actions]

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