Fix quadratic complexity in Reconciler.Reconcile().

[Tener]

Reconciler.Reconcile() is "accidentally quadratic".
For large number of resources N, the running time of this function blows up:

    reconciler_test.go:299: [N=10000] Run time 710.941583ms, time for element 71.094µs
    reconciler_test.go:299: [N=20000] Run time 1.99310675s, time for element 99.655µs
    reconciler_test.go:299: [N=30000] Run time 4.042424417s, time for element 134.747µs
    reconciler_test.go:299: [N=40000] Run time 8.069562916s, time for element 201.739µs
    reconciler_test.go:299: [N=50000] Run time 13.143397s, time for element 262.867µs
    reconciler_test.go:299: [N=100000] Run time 1m13.327041833s, time for element 733.27µs 

This complexity arises because Reconciler.Reconcile() calls both processNewResource and processRegisteredResource N times, and each of those calls currentResources.Find() which also has N complexity. Combined we arrive at NxN=N^2.

After simple fix (switching to map lookup instead of linear list scan):

    reconciler_test.go:299: [N=10000] Run time 296.669375ms, time for element 29.666µs
    reconciler_test.go:299: [N=20000] Run time 575.412375ms, time for element 28.77µs
    reconciler_test.go:299: [N=30000] Run time 840.50825ms, time for element 28.016µs
    reconciler_test.go:299: [N=40000] Run time 1.104382709s, time for element 27.609µs
    reconciler_test.go:299: [N=50000] Run time 1.369955208s, time for element 27.399µs
    reconciler_test.go:299: [N=100000] Run time 2.700222125s, time for element 27.002µs

For increased efficiency and to make it clear reconciler operates on a list of unique resources, I've changed the respective signatures to the new type types.ResourcesWithLabelsMap.

Additionally, two (unused) functions called Find() were removed due to the danger of accidentally repeating the problem in question. collection.ToMap()["foo"] should be used instead.

[codingllama]

Nice.

[espadolini]

what @codingllama said

[zmb3]

Do we still need this type?

[Tener]

Yes, we do: it is rather popular in the codebase. I could work to replace it, but not everywhere ResourcesWithLabelsMap makes sense.