*taskID*.slave.mesos can be an invalid A record.

[drewkerrigan]

When lookup fails in generator.go's slaveRecords for slave.PID.Host, we default to using labels.DomainFrag(slave.PID.Host, labels.Sep, spec) for the rg.SlaveIPs[slave.ID] value.

Later in taskContextRecord, we use that for *taskID*.slave.mesos records. A test case for this and possibly a fix should be created so that invalid A records are not created in this situation.

My suspicion is that a failure would occur later on down the line because resolver.go will attempt a .To4() on all A records which should fail this case.