CLOUDSTACK-1013 : running cloudstack overwrites default public/private ssh keys

The default private/public keypairs in .ssh will not be overwritten.
Instead cloudstack will generate a new keypair id_rsa.cloud and
id_rsa.cloud.pub and use those in developer mode.

To use this insert the (name,value)=(develop,true) tuple into
`cloud`.`configuration`

Signed-off-by: Prasanna Santhanam <tsp@apache.org>