pkg/bisect: recognize lost connection errors

Only select them as relevant if there are not other crash types.

Author: a-nogikh

pkg/bisect/bisect.go

@@ -992,6 +992,11 @@ func mostFrequentReports(reports []*report.Report) (*report.Report, []crash.Type
 			// bisecting this kind of a bug.
 			continue
 		}
+		if info.t == crash.LostConnection && len(perType) > 1 {
+			// This crash type is much more often unrelated than not.
+			// Take it only if it's the only crash type.
+			continue
+		}
 		// Take further crash types until we have considered 2/3 of all crashes, but
 		// no more than 3.
 		needTaken := (crashes + 2) * 2 / 3

pkg/bisect/bisect_test.go

@@ -958,6 +958,34 @@ func TestMostFrequentReport(t *testing.T) {
 			report: "A",
 			other:  true,
 		},
+		{
+			name: "do not take lost connection",
+			reports: []*report.Report{
+				{Title: "A", Type: crash.LostConnection},
+				{Title: "B", Type: crash.Warning},
+				{Title: "C", Type: crash.LostConnection},
+				{Title: "D", Type: crash.Warning},
+				{Title: "E", Type: crash.LostConnection},
+				{Title: "F", Type: crash.Warning},
+			},
+			types:  []crash.Type{crash.Warning},
+			report: "B",
+			other:  true,
+		},
+		{
+			name: "only lost connection",
+			reports: []*report.Report{
+				{Title: "A", Type: crash.LostConnection},
+				{Title: "B", Type: crash.LostConnection},
+				{Title: "C", Type: crash.LostConnection},
+				{Title: "D", Type: crash.LostConnection},
+				{Title: "E", Type: crash.LostConnection},
+				{Title: "F", Type: crash.LostConnection},
+			},
+			types:  []crash.Type{crash.LostConnection},
+			report: "A",
+			other:  false,
+		},
 	}
 	for _, test := range tests {
 		test := test