use ssh paths from tugboat file

my ssh key is ~/.ssh/id_rsa and is named 'trimix' on digital ocean.

trying to find ~/.ssh/trimix[.pem] won't work for me.

could be generalized more, but i'm not super familiar with this code...
Use unix timestamps rather than strings

This means that we can use allocated_at to locate nodes older than x
using a simple solr search, rather than needing to walk every node.
set up rspec
Select and load the correct driver based on URI
ignore generated cruft
add rackspace driver
add openstack driver
add DigitalOcean driver
add aws driver
add cloudstack driver
allow drivers to override default ssh username
allow drivers to pull out creator
remove driver specific code
make ssh username selection actually work
load providers correctly

shift to loading providers on demand, and maintain a registry of
providers
rename drivers to providers
shuffle aws credentials loader
push aws specific stuff into the provider
DRY up loading the correct provider class
note sample fog urls