Ignore dig errors in +short comparisons in tests

Ignore dig errors in +short comparisons in tests

Tests using diff to compare outputs of dig +short shall ignore lines
starting with ";". In dig +short output, such lines should only be
present for errors such as network issues. Since we utilize dig's
default timeout/retry mechanisms, these transitory issues should be
ignored and only the final output should be considered during the diff
comparison.

(cherry picked from commit bd1ef66f836c564ce44c5dacd04d73bb4f36db59)