JCLOUDS-588: Register discovered images in the image cache

Images were cached in memory using a memoized supplier. To allow growing
this cache with the discovered images, the ImageCacheSupplier class has
been created. It provides an in-memory cache with all discovered images
and acts as a view over the image cache that also provides access to
them.

The in-memory cache for the discovered images expires with the session,
just as the image cache does.

The default memoized image supplier has been changed to the
ImageCacheSupplier, to make sure all providers get injected the right
instance, and the old supplier has been qualified with the 'imageCache'
name, in case a provider needs the basic image cache.
JCLOUDS-455: Add get() method to KeyPairApi
JCLOUDS-602 - Add support for volumeType, iops and encrypted to EBS.

Adds CreateVolumeOptions for volume creation, adds support for the
above EBS configs in Image, Volume, BlockDeviceMapping, etc.
JCLOUDS-602. Added live tests for new EBS volume fields.

While they're implemented in apis/ec2, the tests are in
providers/aws-ec2, generally, to make sure ec2-alike clones won't barf
on them. We're exercising creation of volumes, images and instances
with the new options. I also had to do some sketchy wait-and-loop'ing
in AMIAPILiveTest.testCreateAndListEBSBackedImage() due to what seems
to be a delay on new AMIs showing up in filtered DescribeImages calls,
though they'll show up instantly when you specify the image ID. Go figure.