Cider: Direct connection to nREPL fails with totally clean install

[ChelseyM]

Expected behavior

cider-jack-in starts nREPL and connects to it

Actual behavior

nREPL starts, but Cider can't connect to it.

```Making nrepl-create-client-buffer-function local to nrepl-server test while let-bound!
Making nrepl-use-this-as-repl-buffer local to nrepl-server test while let-bound!
Starting nREPL server via /usr/local/bin/lein update-in :dependencies conj [org.clojure/tools.nrepl\ \"0.2.13\"\ \:exclusions\ [org.clojure/clojure]] -- update-in :plugins conj [cider/cider-nrepl\ \"0.16.0\"] -- repl :headless :host ::...
You can run the command ‘cider-jack-in’ with C-c M-j
nREPL server started on 49527
[nREPL] Establishing direct connection to localhost:49527 ...
error in process filter: nrepl--direct-connect: [nREPL] Direct connection to localhost:49527 failed
error in process filter: [nREPL] Direct connection to localhost:49527 failed

## Steps to reproduce the problem

1. Fresh emacs install
1. no .lein/profiles.clj
1. user Cider stable 0.16.0
2. `lein new test`
3. open core.clj
4. `cider-jack-in` 

## Environment & Version information

### CIDER version information

CIDER 0.16.0 (Riga)

### Lein/Boot version

Leiningen 2.8.1 on Java 1.8.0_131 Java HotSpot(TM) 64-Bit Server VM

### Emacs version

GNU Emacs 25.3.1 (x86_64-apple-darwin17.4.0, NS appkit-1561.20 Version 10.13.3 (Build 17D47)) of 2018-01-31
```

Operating system

OS X 10.13.3 (17D47) "High Sierra"

[bbatsov]

Can you tell what localhost is bound to for you?

This reminded me of https://github.com/clojure-emacs/cider/issues/1945

[ChelseyM]

This was a transfer to a new laptop, somehow the /etc/hosts file was completely blank. Restoring it to the OSx default fixed the issue.

##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1 localhost
255.255.255.255 broadcasthost
::1             localhost

Thank you :)