[SPARK-26554][BUILD] Update release-util.sh to avoid GitBox fake 200 headers

## What changes were proposed in this pull request?

Unlike the previous Apache Git repository, new GitBox repository returns a fake HTTP 200 header instead of `404 Not Found` header. This makes release scripts out of order. This PR aims to fix it to handle the html body message instead of the fake HTTP headers. This is a release blocker.

```bash
$ curl -s --head --fail "https://gitbox.apache.org/repos/asf?p=spark.git;a=commit;h=v3.0.0"
HTTP/1.1 200 OK
Date: Sun, 06 Jan 2019 22:42:39 GMT
Server: Apache/2.4.18 (Ubuntu)
Vary: Accept-Encoding
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: POST, GET, OPTIONS
Access-Control-Allow-Headers: X-PINGOTHER
Access-Control-Max-Age: 1728000
Content-Type: text/html; charset=utf-8
```

**BEFORE**
```bash
$ ./do-release-docker.sh -d /tmp/test -n
Branch [branch-2.4]:
Current branch version is 2.4.1-SNAPSHOT.
Release [2.4.1]:
RC # [1]:
v2.4.1-rc1 already exists. Continue anyway [y/n]?
```

**AFTER**
```bash
$ ./do-release-docker.sh -d /tmp/test -n
Branch [branch-2.4]:
Current branch version is 2.4.1-SNAPSHOT.
Release [2.4.1]:
RC # [1]:
This is a dry run. Please confirm the ref that will be built for testing.
Ref [v2.4.1-rc1]:
```

## How was this patch tested?

Manual.

Closes #23476 from dongjoon-hyun/SPARK-26554.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
(cherry picked from commit fe039fa)
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: dongjoon-hyun

dev/create-release/release-util.sh

@@ -73,7 +73,9 @@ function fcreate_secure {
 }
 
 function check_for_tag {
-  curl -s --head --fail "$ASF_REPO_WEBUI;a=commit;h=$1" >/dev/null
+  # Check HTML body messages instead of header status codes. Apache GitBox returns
+  # a header with `200 OK` status code for both existing and non-existing tag URLs
+  ! curl -s --fail "$ASF_REPO_WEBUI;a=commit;h=$1" | grep '404 Not Found' > /dev/null
 }
 
 function get_release_info {