modify cloud-init scripts
change eth0 from dhcp to manual when bridging
lost .cfg extension for some config files
merge with current master
fix strings in tests
Action params now validated at the worker/uniter level

Before the Action is run as a hook on the unit, its passed params are
validated against actions.yaml.  If the validation fails, no error is
produced but the hook will log an error and fail.
Addressed concerns for PR 311
Merge pull request #255 from klyachin/126-maas-bridge

WIP: Modify cloudinit script for MAAS provider

This PR modifies cloudinit upstart scripts, so that network configuration files in MAAS environment has the same structure as in the other environments.

Current configuration:
/etc/network/interfaces:
...
auto eth0
source /etc/network/eth0.config

/etc/network/eth0.config:
iface eth0 inet manual
auto br0
iface br0 inet dhcp
  bridge_ports eth0

New configuration:
/etc/network/interfaces:
...
source /etc/network/interfaces.d/*.cfg

/etc/network/interfaces.d/eth0.cfg:
auto eth0
iface eth0 inet manual

/etc/network/interfaces.d/br0.cfg:
auto br0
iface br0 inet dhcp
Merge pull request #311 from binary132/actions-runhook-validate

Action params now validated at the worker/uniter level

Before the Action is run as a hook on the unit, its passed params are
validated against actions.yaml.  If the validation fails, no error is
produced but the hook will log an error and fail.