Refactor virtual service sync

[stefanprodan]

• detect changes in virtual service with cmp
• ignore destination weight when comparing the two specs
• add tests for virtual service insert, update and config drift

Followup of #51

[codecov-io]

Codecov Report

Merging #54 into master will increase coverage by 0.35%.
The diff coverage is 75%.

@@            Coverage Diff             @@
##           master      #54      +/-   ##
==========================================
+ Coverage   56.34%   56.69%   +0.35%     
==========================================
  Files           9        9              
  Lines        1340     1344       +4     
==========================================
+ Hits          755      762       +7     
+ Misses        452      448       -4     
- Partials      133      134       +1

Impacted Files	Coverage Δ
pkg/controller/router.go	84.95% <75%> (+1.78%)	⬆️

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