Delete the vs/lb pool created for pre-created VPC

[TaoZou1]

The pre-created VPC is shared by many ns. Once the ns deleted, the pre-created VPC will not be deleted.
But the vs/lb pool created for service under pre-created VPC should be released.

Delete vpc/lb pool created for SLB by NCP in cleanup

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 3.96040% with 97 lines in your changes missing coverage. Please review.

Project coverage is 48.06%. Comparing base (8f0c8e4) to head (780fc2a).

Files with missing lines	Patch %	Lines
pkg/nsx/services/vpc/vpc.go	0.00%	83 Missing ⚠️
pkg/nsx/services/vpc/builder.go	0.00%	8 Missing ⚠️
pkg/nsx/services/vpc/store.go	0.00%	4 Missing ⚠️
pkg/clean/clean.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           v4.2.0     #802      +/-   ##
==========================================
- Coverage   48.43%   48.06%   -0.37%     
==========================================
  Files          94       94              
  Lines       11940    12039      +99     
==========================================
+ Hits         5783     5787       +4     
- Misses       5663     5758      +95     
  Partials      494      494              

Flag	Coverage Δ
unit-tests	48.06% <3.96%> (-0.37%)	⬇️

Files with missing lines	Coverage Δ
pkg/nsx/client.go	83.76% <100.00%> (+0.43%)	⬆️
pkg/nsx/services/common/types.go	100.00% <ø> (ø)
pkg/clean/clean.go	0.00% <0.00%> (ø)
pkg/nsx/services/vpc/store.go	71.76% <0.00%> (-3.55%)	⬇️
pkg/nsx/services/vpc/builder.go	83.05% <0.00%> (-13.03%)	⬇️
pkg/nsx/services/vpc/vpc.go	28.20% <0.00%> (-3.36%)	⬇️

[timdengyun]

LGTM

[wenqiq]

LGTM overall. There is a little bit weird that placing the delete operation in the IsSharedVPCNamespaceByNS function.