Add .exe to commands on Windows

Windows cares about extensions. This branch adds .exe suffix to all commands
Actions runHook on worker

This change adds the ability for Actions to be run on a charm using the
same logic used for Hooks.  The Action is run in the "actions" location on the
charm.

A second PR will address Action param Validate.
Removed ActionName and ActionParams from worker/uniter/hook.Info
Pending actions added to worker uniter test
Updated juju/charm dependency to include testable charm with actions location
Added a test to make sure unimplemented Actions don't result in error
Addressed comments on PR 301
Changed from static IP address to dynamic chosen free one.
Quickly fixed one typo of the last PR. ;)
Merge pull request #301 from binary132/actions-runhook-basic

Actions on worker

This change adds the ability for Actions to be run on a charm using the
same logic used for Hooks.  The Action is run in the "actions" location on the
charm.

A second PR will address Action param Validate.
Merge pull request #306 from TheMue/flakey-test-ipv4-ipv6-listening

Fixed flakey TestAPIServerCanListenOnBothIPv4AndIPv6

Test worked with a fixed port which from time to time lead to an error with an alreay used address.
Merge pull request #244 from gabriel-samfira/windows-ensure-symlinks

Add .exe to commands on Windows

On windows, executable commands must have one of the extensions found in $env:PATHEXT. This branch creates a newCommand map where names contain the .exe extension.