Propose to cleanup package dependency (remove hard-coded and add missing)

Hello,

I found hard-coded dependency cause problem when I built package for Debian wheezy.
I suggest to remove all lib* depenency and use dh_shlibdeps that generate library depends automatically.

In addition, I add adduser to depends on this patch because i get following error when installing the package into minimal environment.
```
Setting up td-agent (1.1.20-1.1) ...
/var/lib/dpkg/info/td-agent.postinst: 9: /var/lib/dpkg/info/td-agent.postinst: adduser: not found
dpkg: error processing td-agent (--configure):
 subprocess installed post-installation script returned error exit status 127
Errors were encountered while processing:
 td-agent
E: Sub-process /usr/bin/dpkg returned an error code (1)
```