Add option to fail on control repo unreachable

[andrewfraley]

I didn't see a way to configure this, but if the control repo is unreachable for whatever reason, invalid auth, network, etc., g10k exits 0 with:

WARN: git repository https://myserver/org/r10k.git does not exist or is unreachable at this moment!

I'd like to fail in that case and exit 1.

[xorpaul]

Fixed with https://github.com/xorpaul/g10k/releases/tag/v0.3.9 f26bfa6

From the README.md

abort g10k run if source repository is unreachable

---
:cachedir: '/tmp/g10k'

sources:
  example:
    remote: 'git://github.com/xorpaul/g10k-environment-unavailable.git'
    basedir: '/tmp/example/'
    exit_if_unreachable: true

If you then call g10k with that config file. You should get:

WARN: git repository git://github.com/xorpaul/g10k-environment-unavailable.git does not exist or is unreachable at this moment!
WARNING: Could not resolve git repository in source 'example' (git://github.com/xorpaul/g10k-environment-unavailable.git)

with an exit code 1