[test] Fix flaky FlexCounter.bulkChunksize by replacing usleep with poll-wait#1766

rustiqly merged 1 commit intosonic-net:mastersonic-net/sonic-sairedis:masterfrom

rustiqly:fix/flaky-flexcounter-bulkchunksizerustiqly/sonic-sairedis:fix/flaky-flexcounter-bulkchunksizeCopy head branch name to clipboard