Ticket 49249 - cos_cache is erroneously logging schema checking failure
    
    Bug Description:
        cos is generating virtual attributes in several steps.
        One of the first step is to check that the generated attribute will
        conform the schema.
        Then additional checks (override/merge and cos scope) are performed.
        If the entry does not conform the schema, it skips the additional checks.
        In such case it logs a message stating that the virtual attribute does not
        apply.
        During slapi-log-err refactoring (https://pagure.io/389-ds-base/issue/48978)
        the logging level, in case of schema violation, was move from SLAPI_LOG_PLUGIN
        to SLAPI_LOG_ERR.
    
        This change is incorrect because the potential failure to schema check is
        normal and does not imply the cos would apply to the entry (for example if
        the entry was not in the scope, the cos would also be skipped).
    
    Fix Description:
        Move back the logging level from SLAPI_LOG_ERR to SLAPI_LOG_PLUGIN
    
    https://pagure.io/389-ds-base/issue/49249
    
    Reviewed by: Mark Reynolds
    
    Platforms tested: F23
    
    Flag Day: no
    
    Doc impact: no