Fix pre/post networking parts for SysV and Upstart

[vholer]

Following changes fix the pre/post networking contextualizations introduced by #68 also for legacy platforms. These systems are newly covered:

• CentOS 6 (SysV)
• Debian 8 (SysV)
• Ubuntu 14.04 (Upstart)

plus some small fixes for systemd.

Currently, we generate:

• 2 rpm packages (EL6 and EL7)
• 1 deb package (containing all 3 major init systems support), e.g.:

$ find . | grep -i one-context-local
./usr/lib/systemd/system/one-context-local.service
./etc/init/one-context-local.conf
./etc/init.d/one-context-local

EC2 and Arch Linux support must be checked and refactored as well.