refactor!: consolidate SSH handling

Closes coop-cloud/organising#389.
Closes coop-cloud/organising#341.
Closes coop-cloud/organising#326.
Closes coop-cloud/organising#380.
Closes coop-cloud/organising#360.

cli/internal/cli.go

@@ -378,73 +378,6 @@ var RemoteUserFlag = &cli.StringFlag{
 	Destination: &RemoteUser,
 }
 
-// SSHFailMsg is a hopefully helpful SSH failure message
-var SSHFailMsg = `
-Woops, Abra is unable to connect to connect to %s.
-
-Here are a few tips for debugging your local SSH config. Abra uses plain 'ol
-SSH to make connections to servers, so if your SSH config is working, Abra is
-working.
-
-In the first place, Abra will always try to read your Docker context connection
-string for SSH connection details. You can view your server context configs
-with the following command. Are they correct?
-
-    abra server ls
-
-Is your ssh-agent running? You can start it by running the following command:
-
-    eval "$(ssh-agent)"
-
-If your SSH private key loaded? You can check by running the following command:
-
-    ssh-add -L
-
-If, you can add it with:
-
-    ssh-add ~/.ssh/<private-key-part>
-
-If you are using a non-default public/private key, you can configure this in
-your ~/.ssh/config file which Abra will read in order to figure out connection
-details:
-
-Host foo.coopcloud.tech
-  Hostname foo.coopcloud.tech
-  User bar
-  Port 12345
-  IdentityFile ~/.ssh/bar@foo.coopcloud.tech
-
-If you're only using password authentication, you can use the following config:
-
-Host foo.coopcloud.tech
-  Hostname foo.coopcloud.tech
-  User bar
-  Port 12345
-  PreferredAuthentications=password
-  PubkeyAuthentication=no
-
-Good luck!
-
-`
-
-var ServerAddFailMsg = `
-Failed to add server %s.
-
-This could be caused by two things.
-
-Abra isn't picking up your SSH configuration or you need to specify it on the
-command-line (e.g you use a non-standard port or username to connect). Run
-"server add" with "-d/--debug" to learn more about what Abra is doing under the
-hood.
-
-Docker is not installed on your server. You can pass "-p/--provision" to
-install Docker and initialise Docker Swarm mode. See help output for "server
-add"
-
-See "abra server add -h" for more.
-
-`
-
 // SubCommandBefore wires up pre-action machinery (e.g. --debug handling).
 func SubCommandBefore(c *cli.Context) error {
 	if Debug {