Improving validation step (BUGZ-4238)

• Split validate into two methods - one purely for configuration validation, and the other for config, time and cert as part of startup validation - this is for transparency as arcctl config verify today also contains time and cert checks which is not obvious for the user
  • arcctl config verify which calls the new method validate_config() in Validator.py - which only calls validate_configuration
  • arcctl startup verify is a new control that calls validate_startup which has the same behaviour as the old validate() method, calling validate_configuration(), validate_time() and validate_certificates()).
• For the certificate check - remove --check option as this might take too long in some situations. The important for the validation is just to check that the file is not corrupted, and then --check is not needed