set the inventory dir as the default inventory

Which will allow both static and dynamic inventories to be placed here.
move the ec2 dynamic inventory files into inventory dir
update use of ebs vars

Putting them into the <environment>-az file.
be nice and already include the dir nav up to the parent dir

From where you would expect to run the `ansible-playbook` command.
update README for combining of inventories
Merge pull request #2 from donal/combine-ansible-inventories

Combine static and dynamic (ec2) inventories