Merge branch 'specify-working-directory' into 'master'

Add `-C` option to specify the working directory

The concrete goal of adding this switch is to be able to start a runner as:

```
/opt/gitlab-runner/bin/runner -C /home/gitlab-runner
```

This way we can keep the runner's executable code under `/opt/gitlab-runner`, owned by root, and have `/home/gitlab-runner` (or whatever we come up with) as a writable, working area for the gitlab-ci-runner user.

This new switch does not change the default behavior of the runner.

See merge request !14

CHANGELOG

+v5.1.0
+  - Add `-C` command-line option to specify the working directory
+
 v5.0.0
   - Async command execution
   - All commands executed as single bash script from tempfile

README.md

@@ -97,6 +97,13 @@ CI_SERVER_URL=https://ci.example.com REGISTRATION_TOKEN=replaceme bundle exec ./
 The registration token can be found at: <http://gitlab-ci-domain.com/admin/runners>, accessible through Header > Runners.
+By default the configuration file for your new runner gets written in the directory where the gitlab-ci-runner source code was installed, e.g. in `/home/gitlab_ci_runner/gitlab-ci-runner/config.yml`.
+You can tell `bin/setup` to use a different directory with the `-C` switch.
+
+```
+bin/setup -C /my/runner/working/directory
+```
+
 #### Create an Upstart job (Ubuntu, Centos 6)
 ```
@@ -135,6 +142,13 @@ cd /home/gitlab_ci_runner/gitlab-ci-runner
 bundle exec ./bin/runner
 ```
+If you are using a custom working directory you can tell the runner about it with the `-C` switch.
+The default working directory is the directory where the gitlab-ci-runner source code was installed, e.g. `/home/gitlab_ci_runner/gitlab-ci-runner`.
+
+```
+bundle exec bin/runner -C /my/runner/working/directory
+```
+
 ### Update
 In order to update the runner to a new version just go to runner directory and do next: 

lib/config.rb

 require 'yaml'
-ROOT_PATH = File.expand_path(File.join(File.dirname(__FILE__), ".."))
+require 'optparse'
+# The default root path is the path where the gitlab-ci-runner source got
+# installed. This may be overridden by the OptionParser below.
+$root_path = File.expand_path(File.join(File.dirname(__FILE__), ".."))
 module GitlabCi
   class Config
@@ -23,7 +26,7 @@ module GitlabCi
     end
     def builds_dir
-      @builds_path ||= File.join(ROOT_PATH, 'tmp', 'builds')
+      @builds_path ||= File.join($root_path, 'tmp', 'builds')
     end
     def write(key, value)
@@ -37,7 +40,13 @@ module GitlabCi
     private
     def config_path
-      File.join(ROOT_PATH, 'config.yml')
+      File.join($root_path, 'config.yml')
     end
   end
 end
+
+OptionParser.new do |opts|
+  opts.on('-CWORKING_DIRECTORY', 'Specify the working directory for gitlab-ci-runner') do |v|
+    $root_path = File.expand_path(v)
+  end
+end.parse!