The documentation for validate_vendor_used in hack/validate/vendor states
that a warning will be emitted if license information cannot be found in
a vendored package. However, because the script is run with pipefail set
(owing to the inclusion of the common validation script .validate) and
`grep -c` is used, the entire script will fail whenever license information
cannot be found in a vendored package.

Signed-off-by: Chris Price <cprice@mirantis.com>