Improve multi-cluster unit test

[luolanzone]

Add more unit tests for multi-cluster and remove some dead codes.

For #4142
Signed-off-by: Lan Luo luola@vmware.com

[luolanzone]

/test-multicluster-e2e

[luolanzone]

/test-multicluster-e2e

[luolanzone]

/test-multicluster-e2e

[codecov]

Codecov Report

Merging #4158 (8163b7e) into main (3696543) will increase coverage by 0.91%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #4158      +/-   ##
==========================================
+ Coverage   65.92%   66.84%   +0.91%     
==========================================
  Files         304      315      +11     
  Lines       46626    46655      +29     
==========================================
+ Hits        30737    31185     +448     
+ Misses      13487    13045     -442     
- Partials     2402     2425      +23     

Flag	Coverage Δ
e2e-tests	58.68% <ø> (?)
integration-tests	34.94% <ø> (+<0.01%)	⬆️
kind-e2e-tests	49.46% <ø> (+0.41%)	⬆️
unit-tests	45.05% <ø> (+0.09%)	⬆️

Impacted Files	Coverage Δ
...icluster/controllers/multicluster/common/helper.go	88.23% <ø> (+30.23%)	⬆️
pkg/ovs/ovsctl/ofctl.go	46.57% <0.00%> (-5.48%)	⬇️
pkg/agent/controller/networkpolicy/reject.go	77.50% <0.00%> (-3.50%)	⬇️
pkg/agent/route/route_linux.go	50.21% <0.00%> (-2.98%)	⬇️
pkg/agent/openflow/multicluster.go	44.85% <0.00%> (-1.87%)	⬇️
pkg/controller/externalippool/controller.go	83.03% <0.00%> (-1.79%)	⬇️
pkg/flowaggregator/flowaggregator.go	68.31% <0.00%> (-1.74%)	⬇️
pkg/agent/util/iptables/iptables.go	45.07% <0.00%> (-1.56%)	⬇️
pkg/util/k8s/node.go	80.90% <0.00%> (-0.91%)	⬇️
pkg/agent/openflow/network_policy.go	78.49% <0.00%> (-0.87%)	⬇️
... and 48 more

[jianjuns]

/skip-all