order create with secret.bit_length=None returns 201 (expected 400)

Running Cafe test test_negative_create_order_w_bit_length_null which creates an order with a secret with bit_length set to None. It expects to get back an http 400 error.

Prior to https://review.openstack.org/#/c/102009/4 this test passed by getting an http 400 back from the order POST.

After that fix the test gets back an http 201 which causes the test to fail.

The validation for secrets schema validation passes, then the check for the value of the bit_length uses the default (0) which passes the updated tests (looking for mod 8). Previous test also looked for < 0.

One suggestion for a fix is to check for the bit_length == 0 after we get it out of the secret.

See https://review.openstack.org/#/c/102009/4/barbican/common/validators.py