cleanup: update error msg when join cluster failed

[chaosi-zju]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

cleanup: update error msg when join cluster failed

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[karmada-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 42.32%. Comparing base (057cf86) to head (e32864f).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/karmadactl/join/join.go	0.00%	2 Missing ⚠️

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5774   +/-   ##
=======================================
  Coverage   42.31%   42.32%           
=======================================
  Files         655      655           
  Lines       55756    55757    +1     
=======================================
+ Hits        23591    23597    +6     
+ Misses      30651    30648    -3     
+ Partials     1514     1512    -2     

Flag	Coverage Δ
unittests	42.32% <0.00%> (+<0.01%)	⬆️

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[Rains6]

karmadactl as a command line tool provides more prompt information to guide users to solve problems by themselves. lgtm

[karmada-bot]

@Rains6: changing LGTM is restricted to collaborators

In response to this:

/lgtm

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