playground: don't get Pid() when there is no Process

[dveeden]

What problem does this PR solve?

Closes #1932

> main.(*Playground).terminate() ./components/playground/playground.go:990 (hits goroutine(1):1 total:1) (PC: 0x150724e)
   985:	
   986:		if p.grafana != nil {
   987:			go kill("grafana", p.grafana.cmd.Process.Pid, p.grafana.wait)
   988:		}
   989:		for _, inst := range p.tiflashs {
=> 990:			fmt.Printf("inst: %-v\n", inst.Pid())
   991:			kill(inst.Component(), inst.Pid(), inst.Wait)
   992:		}
   993:		for _, inst := range p.ticdcs {
   994:			kill(inst.Component(), inst.Pid(), inst.Wait)
   995:		}
(dlv) p inst
*github.com/pingcap/tiup/components/playground/instance.TiFlashInstance {
	instance: github.com/pingcap/tiup/components/playground/instance.instance {
		ID: 0,
		Dir: "/home/dvaneeden/.tiup/data/T9HJm1o/tiflash-0",
		Host: "127.0.0.1",
		Port: 8123,
		StatusPort: 8234,
		ConfigPath: "",
		BinPath: "",},
	TCPPort: 9000,
	ServicePort: 3930,
	ProxyPort: 20170,
	ProxyStatusPort: 20292,
	ProxyConfigPath: "",
	pds: []*github.com/pingcap/tiup/components/playground/instance.PDInstance len: 1, cap: 1, [
		*(*"github.com/pingcap/tiup/components/playground/instance.PDInstance")(0xc000200b40),
	],
	dbs: []*github.com/pingcap/tiup/components/playground/instance.TiDBInstance len: 1, cap: 1, [
		*(*"github.com/pingcap/tiup/components/playground/instance.TiDBInstance")(0xc000172d80),
	],
	Process: github.com/pingcap/tiup/components/playground/instance.Process nil,}

What is changed and how it works?

Check List

Tests

• Manual test (add detailed scripts or steps below)

Related changes

• Need to cherry-pick to the release branch

Release notes:

Playground no longer panics when trying to stop processes that don't actually exist

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[codecov-commenter]

Codecov Report

Merging #1933 (b5422cf) into master (44a1257) will decrease coverage by 31.42%.
The diff coverage is 0.00%.

❗ Current head b5422cf differs from pull request most recent head 452ea85. Consider uploading reports for the commit 452ea85 to get more accurate results

@@             Coverage Diff             @@
##           master    #1933       +/-   ##
===========================================
- Coverage   52.44%   21.02%   -31.42%     
===========================================
  Files         307      237       -70     
  Lines       35532    29981     -5551     
===========================================
- Hits        18633     6303    -12330     
- Misses      14703    23074     +8371     
+ Partials     2196      604     -1592     

Flag	Coverage Δ
cluster	?
dm	?
playground	?
tiup	?
unittest	21.02% <0.00%> (-<0.01%)	⬇️

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

Impacted Files	Coverage Δ
components/playground/playground.go	0.00% <0.00%> (-49.48%)	⬇️
main.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/meta/paths.go	0.00% <0.00%> (-100.00%)	⬇️
components/dm/main.go	0.00% <0.00%> (-100.00%)	⬇️
components/cluster/main.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/cluster/task/builder.go	0.00% <0.00%> (-100.00%)	⬇️
components/dm/spec/bindversion.go	0.00% <0.00%> (-100.00%)	⬇️
pkg/cluster/template/scripts/scripts.go	0.00% <0.00%> (-100.00%)	⬇️
components/dm/spec/cluster.go	0.00% <0.00%> (-91.67%)	⬇️
pkg/cluster/spec/bindversion.go	0.00% <0.00%> (-90.91%)	⬇️
... and 251 more

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[AstroProfundis]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: b5422cf

[ti-chi-bot]

@dveeden: Your PR was out of date, I have automatically updated it for you.

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