Feat/neighbour limit

[clementnuss]

instead of querying all (valid) neighbouring pods, we filter and
only query KUBENURSE_NEIGHBOUR_LIMIT other neighbours.
the algorithm is implemented as follows:

• hashes are the first 64bits of sha256.Sum(...)
• we subtract the current node's hash from every other node name hash (so the smallest hashes will be the "closest" hashes to the current node)
• we put those subtracted hashes in a max-heap
• every time the heap grows larger than the neighbourhood_limit, we pop the max element

thus at the end, the heap contains the 10 next neighbour nodes for our current node

[coveralls]

Pull Request Test Coverage Report for Build 8282544160

Details

• 65 of 82 (79.27%) changed or added relevant lines in 5 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-5.1%) to 64.048%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/servicecheck/neighbours.go	51	54	94.44%
internal/kubenurse/server.go	7	11	63.64%
internal/servicecheck/httptrace.go	3	13	23.08%

Files with Coverage Reduction	New Missed Lines	%
internal/servicecheck/httptrace.go	1	38.64%
internal/servicecheck/neighbours.go	1	88.17%

Totals
Change from base Build 8154839966:	-5.1%
Covered Lines:	424
Relevant Lines:	662

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💛 - Coveralls

[zbindenren]

LGTM.

Maybe add in a later MR a metric when a node is not getting scaped.