*: not use a fixed port number

[rleungx]

What problem does this PR solve?

Issue Number: ref #7969

What is changed and how does it work?

To fix the following error:

$ make ut
cd tools && GOEXPERIMENT= CGO_ENABLED=0 go build -tags xprog -gcflags '' -ldflags '-X "github.com/tikv/pd/pkg/versioninfo.PDReleaseVersion=v8.3.0-alpha-26-g80f74bfc3" -X "github.com/tikv/pd/pkg/versioninfo.PDBuildTS=2024-08-08 07:31:05" -X "github.com/tikv/pd/pkg/versioninfo.PDGitHash=80f74bfc3af5e18b368134d8ed96f2a7c13ca33c" -X "github.com/tikv/pd/pkg/versioninfo.PDGitBranch=leak" -X "github.com/tikv/pd/pkg/versioninfo.PDEdition=Community" -X "github.com/pingcap/tidb-dashboard/pkg/utils/version.InternalVersion=8.3.0-e6e78c7c" -X "github.com/pingcap/tidb-dashboard/pkg/utils/version.Standalone=No" -X "github.com/pingcap/tidb-dashboard/pkg/utils/version.PDVersion=v8.3.0-alpha-26-g80f74bfc3" -X "github.com/pingcap/tidb-dashboard/pkg/utils/version.BuildTime=2024-08-08 07:31:05" -X "github.com/pingcap/tidb-dashboard/pkg/utils/version.BuildGitHash=e6e78c7c120b"' -o /data/nvme0n1/ryan/workspace/pd/bin/xprog pd-ut/xprog.go
cd tools && GOEXPERIMENT= CGO_ENABLED=0 go build -gcflags '' -ldflags '-X "github.com/tikv/pd/pkg/versioninfo.PDReleaseVersion=v8.3.0-alpha-26-g80f74bfc3" -X "github.com/tikv/pd/pkg/versioninfo.PDBuildTS=2024-08-08 07:31:06" -X "github.com/tikv/pd/pkg/versioninfo.PDGitHash=80f74bfc3af5e18b368134d8ed96f2a7c13ca33c" -X "github.com/tikv/pd/pkg/versioninfo.PDGitBranch=leak" -X "github.com/tikv/pd/pkg/versioninfo.PDEdition=Community" -X "github.com/pingcap/tidb-dashboard/pkg/utils/version.InternalVersion=8.3.0-e6e78c7c" -X "github.com/pingcap/tidb-dashboard/pkg/utils/version.Standalone=No" -X "github.com/pingcap/tidb-dashboard/pkg/utils/version.PDVersion=v8.3.0-alpha-26-g80f74bfc3" -X "github.com/pingcap/tidb-dashboard/pkg/utils/version.BuildTime=2024-08-08 07:31:06" -X "github.com/pingcap/tidb-dashboard/pkg/utils/version.BuildGitHash=e6e78c7c120b"' -o /data/nvme0n1/ryan/workspace/pd/bin/pd-ut pd-ut/ut.go pd-ut/coverProfile.go
# only run unit tests
./bin/pd-ut run --ignore tests --race --junitfile ./junitfile
2024/08/08 15:31:10 maxprocs: Leaving GOMAXPROCS=72: CPU quota undefined
[2024/08/08 15:31:10.938 +08:00] [FATAL] [server.go:51] ["server listen error"] [error="listen tcp 0.0.0.0:20180: bind: address already in use"] [stack="github.com/tikv/pd/tools/pd-ut/alloc.RunHTTPServer.func2\n\t/data/nvme0n1/ryan/workspace/pd/tools/pd-ut/alloc/server.go:51"]
make: *** [Makefile:231: ut] Error 1

Check List

Tests

• No code

Release note

None.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: HuSharp, okJiang

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [HuSharp]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-08 07:37:28.830897367 +0000 UTC m=+510378.697996453: ☑️ agreed by HuSharp.
• 2024-08-08 07:39:04.813920233 +0000 UTC m=+510474.681019321: ☑️ agreed by okJiang.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.47%. Comparing base (ff71512) to head (9de05a8).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8506   +/-   ##
=======================================
  Coverage   77.46%   77.47%           
=======================================
  Files         472      472           
  Lines       61795    61800    +5     
=======================================
+ Hits        47867    47877   +10     
+ Misses      10371    10367    -4     
+ Partials     3557     3556    -1     

Flag	Coverage Δ
unittests	77.47% <ø> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.