common: Client agent installers for POSIX platforms

A new agents generator creates agents installers for:
- MAC OS X
- Debian based distributions (tested on Debian Wheezy and Ubuntu 14.04)
- RPM based distributions (tested on CentOS 5.6)

Each package includes an installer of:
- fusioninventory-agent
- openssh-server
- tightvncserver (for .deb packages)
- tigervnc-server (for .rpm packages)

Post-install actions:
- Fusion inventory config file will be updated with a correct server URL
  and immediatelly launched to send a first inventory.
- SSH public key of Pulse2 server will be added to authorized_keys.

For linux platforms, a package without vnc server dependency will be
generated, it will be useful for machines without X server.