WebSocket tests are flaky

[benmanns]

When working on #244 and #245, I noticed that the tests can fail successfully if no messages are produced.

@test "websocket-connector-test" {
    count=1
    echo "Starting consumer on topic $TOPIC"
    sleep 13

    fluvio consume -B -d $TOPIC | while read input; do
        expected="Hello, Fluvio! - $count"
        echo $input = $expected
        [ "$input" = "$expected" ]
        count=$(($count + 1))
        if [ $count -eq 10 ]; then
            break;
        fi
    done

}

If fluvio consume -B -d $TOPIC produced no lines, nothing gets tested. I tested a new method that I think works pretty well:

@test "websocket-connector-test" {
    count=1
    echo "Starting consumer on topic $TOPIC"
    sleep 13

    expected=<<EOF
Hello, Fluvio! - 1
Hello, Fluvio! - 2
Hello, Fluvio! - 3
Hello, Fluvio! - 4
Hello, Fluvio! - 5
Hello, Fluvio! - 6
Hello, Fluvio! - 7
Hello, Fluvio! - 8
Hello, Fluvio! - 9
Hello, Fluvio! - 10
EOF

    run fluvio consume -B -d $TOPIC

    [[ $output = $expected* ]]
}

I check against $expected as a prefix because the tests tend to exit and re-run which duplicates the output.