Incorrect error message displayed

[nitinbodke]

My "/tmp" directory had "consul" binary, leftover from "consul" installation.
Executed following command from the path where I copied it:

[admin@localhost local]$ consul agent -server -bootstrap-expect 1 \
>     -data-dir /tmp/consul -node=agent-one -bind=10.0.2.15 \
>     -config-dir /etc/consul.d

Expected:
Consul should differentiate between "consul" binary and directory.
And should give proper error message.

Actual Result:

==> CRITICAL: Deprecated data folder found at "/tmp/consul/mdb"!
==> Consul will refuse to boot with this directory present.
==> See https://www.consul.io/docs/upgrade-specific.html for more information.

[mckennajones]

@slackpad What should the expected behavior be in this case? Should consul error out if the -data-dir points to a consul binary?

[slackpad]

We should stat the -data-dir and give a "not a directory" message if IsDir() is false.

[slackpad]

Despite what I said in #2529 (comment), during some testing with this change merge I realized I think we were auto-creating the directory before, so this might be a regression. @kyhavlov will take a look; pulling into the 0.7.2 release milestone.