Fix wrong evaluation of attributes in check_repl_update
    
    The method check_repl_update in ipaserver/install/replication.py badly
    handles the attributes nsds5ReplicaLastUpdateStart and
    nsds5ReplicaLastUpdateEnd as it expects them to contain an int.
    These attributes are defined as GeneralizedTime
    (OID 1.3.6.1.4.1.1466.115.121.1.24, for instance
    nsds5ReplicaLastUpdateEnd='20190412122523Z') but older versions of 389-ds can
    also return the value 0 for uninitialized values (see 389-ds ticket 47836).
    The code must be able to handle the generalized time format or the 0 value.
    
    The fix removes the 'Z' from the GeneralizedTime and converts to an int,
    or assigns 0.
    
    Fixes: https://pagure.io/freeipa/issue/7909
    Reviewed-By: François Cami <fcami@redhat.com>