avocado.utils.remote: Add timeout and attempts.

Add options to control remote timeout and the number of attempts
to connect.

Add 'remote_capable' feature.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
Merge pull request #93 from ruda/remote_timeout_attempts_capable

avocado.utils.remote: Add conenction timeout and attempts and remote_capable