fix(storage-node): fix get username and password from dbClass

[yikuaibro]

Type of change:

• Bugfix
• New feature provided
• Improve performance
• Backport patches

What this PR does / why we need it:

fix #292 (comment) - the first point

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[yikuaibro]

@Xu-Wentao help review

[codecov-commenter]

Codecov Report

Merging #386 (1b50b85) into main (e52f093) will decrease coverage by 1.56%.
The diff coverage is 5.26%.

@@            Coverage Diff             @@
##             main     #386      +/-   ##
==========================================
- Coverage   47.34%   45.78%   -1.56%     
==========================================
  Files          48       49       +1     
  Lines        5264     5452     +188     
==========================================
+ Hits         2492     2496       +4     
- Misses       2547     2731     +184     
  Partials      225      225              

Impacted Files	Coverage Δ
pitr/cli/internal/cmd/backup.go	73.47% <0.00%> (ø)
...tor/cmd/shardingsphere-operator/manager/manager.go	0.00% <ø> (ø)
...perator/pkg/controllers/compute_node_controller.go	0.00% <0.00%> (ø)
...phere-operator/pkg/controllers/proxy_controller.go	0.00% <ø> (ø)
...operator/pkg/controllers/proxyconfig_controller.go	0.00% <ø> (ø)
...pkg/controllers/shardingsphere_chaos_controller.go	46.46% <ø> (ø)
...operator/pkg/distsql/visitor/shadow_rdl_visitor.go	0.00% <0.00%> (ø)
...operator/pkg/reconcile/computenode/compute_node.go	38.29% <50.00%> (ø)
...perator/pkg/controllers/storage_node_controller.go	55.85% <87.50%> (+0.40%)	⬆️
...ator/cmd/shardingsphere-operator/manager/option.go	49.52% <100.00%> (ø)

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