Use augeas instead of sysctl::value

We don't actually need to execute 'sysctl -w' for
net.bridge.bridge-nf-call* sysctl keys since this can cause
puppet errors if puppet tries to apply sysctl::value before bridge
kernel module is loaded.

So we just need to make sure those sysctl keys are configured
properly in /etc/sysctl.conf file. When bridge kernel module is
loaded by libvirt, it will set them to correct values itself.

Closes-bug: #1401100
Change-Id: Ib53038bc53846d14a6c7bf028c7b4e78eef56255
Merge "Use augeas instead of sysctl::value" into stable/5.1