tools: Resolve hosts in --ldap-servers in engine-manage-domains

Tries to resolve hosts specified in argument --ldap-servers during
add/edit action in engine-manage-domains. If some host cannot be
resolved, warning is logged and displayed in console.

Change-Id: Ibae81ccd6b2a402c856934839f1dbdad316bbc3d
Bug-URL: https://bugzilla.redhat.com/1001976
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Martin Perina <mperina@redhat.com>