Pass -oUseRoaming=no by default, provide facilities to pass different options per identity, and to debug the generated command.
Pass -oUseRoaming=no by default, provide facilities to pass different
options per identity, and to debug the generated command.

In this change:

- introduced a few more configuration parameters to have
  default flags passed to ssh, and per identity flags.

- when VERBOSITY=LOG_DEBUG ssh-ident is called, the generated
  ssh command is now displayed. Used to verify correct
  behavior of code.

ccontavalli/ssh-ident