Provide error if -ui and -ui-dir are both specified

[slackpad]

This does a rebase of #2577 and tweaks the wording.

Closes #2577, #2903, #2576.

[tylerwalts]

This breaks for me on Windows, between using release 0.8.0 and 0.8.5. I do not use ui_dir (only ui set to true) in the config. Since upgrading, I now get that (incorrect) error message, and now it will not launch. Even adding in a line for "ui_dir": "" with blank string value I thought might work after looking at the diff, but does not. Maybe there is a default or something that only happens on Windows?

[slackpad]

@tylerwalts that's super strange - there's no special treatment of ui-dir on Windows that I can find. Is it possible you have a stray config file that's maybe getting picked up?

[tylerwalts]

Thanks for the quick response! I verified no other config files exist, and simplified it down to this only to still reproduce the symptom:

{
  "addresses": {
    "http": "0.0.0.0"
  },
  "advertise_addr": "192.168.1.123",
  "datacenter": "foo",
  "log_level": "info",
  "node_name": "bar",
  "server": true,
  "ui": true
}

Results in log:

==> Both the ui and ui-dir flags were specified, please provide only one

EDIT/SOLVED: I forgot to mention that I am using choco to install and manage consul via nssm, and looking deeper into how it is launched I see that the CLI is passing the ui-dir arg in. Sorry for the false alarm and I'll leave this up in case anyone else has a similar issue:

My "fix" is to remove the "ui": true from my config, since the CLI arg sets the UI path out of box and it is redundant. Everything working as expected now 👍

[slackpad]

@tylerwalts thanks for checking - opened #3229 to track this since this is a PR - I think we will need to fire up Windows and trace through this a bit; I can't think of any mechanism that would cause this.