Avoid prompts while installing a package

If the old package (and config file) is already installed, prompt is displayed during execution of the init script.
So, I fixed to be installed config file for the new version at all times. 

e.g.
```
03:06:43 + apt-get install -f -y --force-yes --no-install-recommends runit
03:06:43 Reading package lists...
03:06:43 Building dependency tree...
03:06:43 Reading state information...
03:06:43 Suggested packages:
03:06:43   socklog-run
03:06:43 The following packages will be upgraded:
03:06:43   runit
03:06:43 1 upgraded, 0 newly installed, 0 to remove and 182 not upgraded.
03:06:43 Need to get 107 kB of archives.
03:06:43 After this operation, 179 kB disk space will be freed.
03:06:43 Get:1 http://ap-northeast-1.ec2.archive.ubuntu.com/ubuntu/ precise-updates/universe runit amd64 2.1.1-6.2ubuntu2.1 [107 kB]
03:06:44 Fetched 107 kB in 0s (2,021 kB/s)
03:06:44 (Reading database ... 90722 files and directories currently installed.)
03:06:44 Preparing to replace runit 2.1.1-6.2ubuntu2 (using .../runit_2.1.1-6.2ubuntu2.1_amd64.deb) ...
03:06:44 runsvdir stop/waiting
03:06:44 Unpacking replacement runit ...
03:06:44 Processing triggers for man-db ...
03:06:45 Processing triggers for ureadahead ...
03:06:45 Setting up runit (2.1.1-6.2ubuntu2.1) ...
03:06:45 
03:06:45 Configuration file `/etc/init/runsvdir.conf'
03:06:45  ==> File on system created by you or by a script.
03:06:45  ==> File also in package provided by package maintainer.
03:06:45    What would you like to do about it ?  Your options are:
03:06:45     Y or I  : install the package maintainer's version
03:06:45     N or O  : keep your currently-installed version
03:06:45       D     : show the differences between the versions
03:06:45       Z     : start a shell to examine the situation
03:06:45  The default action is to keep your current version.
03:06:45 *** runsvdir.conf (Y/I/N/O/D/Z) [default=N] ?
```