Handle NotFound, Forbidden, Auth errors

Changes:
* hide stack trace for known exceptions
* show stack trace when -v / --verbose option is used as well
Fix 'td import:create' with import-only permission

Changes:
* Remove client validation for db and table to avoid incurring
  in a failure because an API key that has import only permissions
  to a database cannot list tables. The validation on whether
  the table exists is deferred to the APIs (server side validation)