enhanced role permission validation

this commit avoid incompleted permission keys. For example command:
osm role-update --add "vim_accoun: true"
must fais, as it should be "vim_accounts: true"

Change-Id: Ib5a5d88ae35120e99a43c80d20ccf8b207701780
Signed-off-by: tierno <alfonso.tiernosepulveda@telefonica.com>