fix: Avoid allocating repeated IP to machines

[codecov[bot]]

Codecov Report

Merging #25 (40af3ae) into main (37ae04d) will decrease coverage by 1.71%. The diff coverage is 30.76%.

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
- Coverage   52.92%   51.20%   -1.72%     
==========================================
  Files           3        3              
  Lines         427      496      +69     
==========================================
+ Hits          226      254      +28     
- Misses        170      200      +30     
- Partials       31       42      +11     

Impacted Files	Coverage Δ
controllers/virtinkcluster_controller.go	41.63% <26.31%> (-10.89%)	:arrow_down:
controllers/virtinkmachine_controller.go	53.27% <42.85%> (+7.24%)	:arrow_up:

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[scuzhanglei]

I'm still not sure if we should DIY IP allocation in this project. Could we pend this PR first and try the metal3's ip address manager first?

okay, I will submit another PR to compare.

[scuzhanglei]

new PR #28