Ignore "communications error" in unknown system test

Job #3125906 failed:

I:unknown:querying for various representations of an IN TXT record (2)
0a1
> ;; communications error to 10.53.0.1#13008: timed out
I:unknown:#4 failed
I:unknown:querying for various representations of an IN TYPE123 record (3)
I:unknown:querying for NULL record (4)
I:unknown:querying for empty NULL record (5)
0a1,2
> ;; communications error to 10.53.0.1#13008: timed out
> ;; communications error to 10.53.0.1#13008: timed out
I:unknown:failed

This is because under IO pressure DiG fails to connect to named on the first time and ;; communications error to 10.53.0.1#13008: timed out appears in the DiG output log and fails comparison to the expected "hello" string.

The unknown system test could just ignore ;; communications error to 10.53.0.1#13008: timed out.