Increase read/write timeouts in the docker hypervisor

This change increases the read and write timeouts to the docker api.
By default this is 60 seconds

Additionally we use the version assertion from docker-api so we
don't try and talk to an incompatible api version.
Install ssh clients in the docker hypervisor

Some docker base images are seriously stripped down and will not
include the ssh client packages.  These are normally where the scp
and sftp binaries live which are needed in later provisioning steps.
Refactor the flow of platform specific actions

The previous flow (using the return value from the case statement) was
needlessly complex and caused some confusion.  Refactor to add more explicit
appends to the dockerfile variable in each when block.
Update README to reflect changes to docker hypervisor