rgw: always check if token is expired

rgw: always check if token is expired

Fixes: #11367
Currently token expiration is only checked by the token cache. With PKI
tokens no expiration check is done after decoding the token. This causes
PKI tokens to be valid indefinitely. UUID tokens are validated by
keystone after cache miss so they are not affected by this bug.

This commit adds explicit token expiration check to
RGWSwift::validate_keystone_token()

Signed-off-by: Anton Aksola <anton.aksola@nebula.fi>
Reported-by: Riku Lehto <riku.lehto@nexetic.com>