xci: playbooks: Fix synchronization of external scenarios

xci: playbooks: Fix synchronization of external scenarios

The code was supposed to copy everything from
{{ xci_path }}/{{ scenario.role }} to the XCI roles directory but
external scenarios have their 'role' attribute relative to their
repository whereas internal one have it relative to the {{ xci_path }}.
As such, changes to external scenarios were not copied successfully
to the playbooks directory and their changes where never tested.
This removes the 'xci/scenarios/$scenario' part of the inbound
roles attribute to make all them relative to the
xci/scenarios/$scenario directory.

Change-Id: Id28671b30c8ee4aa6bc186444c0e5a3a3ea3d89b
Signed-off-by: Markos Chandras <mchandras@suse.de>