fix: Ignore duplicate IIS entries from Perflib

Perflib often exposes duplicate IIS entries, suffixed with '#' and a
number (I.E. iis_site_name#1).
These duplicate entries were causing the exporter to fail scraping due
to duplicate metrics.

Based on user feedback, the entry with the highest suffix
value is kept, with other duplicate entries discarded.

E.G. Given the following list of site names, "Site_B" would be
discarded, and "Site_B#2" would be kept and presented as "Site_B" in the
collector metrics.
[ "Site_A", "Site_B", "Site_C", "Site_B#2" ]

Signed-off-by: Ben Reedy <breed808@breed808.com>

collector/iis_test.go

@@ -1,9 +1,49 @@
 package collector
 
 import (
+	"reflect"
 	"testing"
 )
 
 func BenchmarkIISCollector(b *testing.B) {
 	benchmarkCollector(b, "iis", newIISCollector)
 }
+
+func TestIISDeduplication(t *testing.T) {
+	start := []perflibAPP_POOL_WAS{
+		{
+			Name:             "foo",
+			Frequency_Object: 1,
+		},
+		{
+			Name:             "foo1#999",
+			Frequency_Object: 2,
+		},
+		{
+			Name:             "foo#2",
+			Frequency_Object: 3,
+		},
+		{
+			Name:             "bar$2",
+			Frequency_Object: 4,
+		},
+		{
+			Name:             "bar_2",
+			Frequency_Object: 5,
+		},
+	}
+	var expected = make(map[string]perflibAPP_POOL_WAS)
+	// Should be deduplicated from "foo#2"
+	expected["foo"] = perflibAPP_POOL_WAS{Name: "foo#2", Frequency_Object: 3}
+	// Map key should have suffix stripped, but struct name field should be unchanged
+	expected["foo1"] = perflibAPP_POOL_WAS{Name: "foo1#999", Frequency_Object: 2}
+	// Map key and Name should be identical, as there is no suffix starting with "#"
+	expected["bar$2"] = perflibAPP_POOL_WAS{Name: "bar$2", Frequency_Object: 4}
+	// Map key and Name should be identical, as there is no suffix starting with "#"
+	expected["bar_2"] = perflibAPP_POOL_WAS{Name: "bar_2", Frequency_Object: 5}
+
+	deduplicated := dedupIISNames(start)
+	if !reflect.DeepEqual(expected, deduplicated) {
+		t.Errorf("Flattened values do not match!\nExpected result: %+v\nActual result: %+v", expected, deduplicated)
+	}
+}