[make-rules] test grep should treat binary as text

The output of `go test` is passed throug a grep filter that's used when
producing junit output.  Unfortunately, when testing round-trip
conversions with random strings, grep can become convinced that the test
output is binary, and will truncate a failed test before any output is
displayed, showing "binary file (standard input) matches".

This forces grep to consider test output to be text, so that we always
see test results.

hack/make-rules/test.sh

@@ -289,7 +289,7 @@ runTests() {
       ${KUBE_RACE} ${KUBE_TIMEOUT} "${@}" \
      "${testargs[@]:+${testargs[@]}}" \
      | tee ${junit_filename_prefix:+"${junit_filename_prefix}.stdout"} \
-     | grep "${go_test_grep_pattern}" && rc=$? || rc=$?
+     | grep --binary-files=text "${go_test_grep_pattern}" && rc=$? || rc=$?
     produceJUnitXMLReport "${junit_filename_prefix}"
     return ${rc}
   fi