Add support for Go recovered panics

Author: kasparjarek

lib/fluent/plugin/exception_detector.rb

@@ -94,7 +94,7 @@ def self.supported
     ].freeze
 
     GO_RULES = [
-      rule(:start_state, /\bpanic: /, :go_after_panic),
+      rule([:start_state, :go_after_panic], /\bpanic: /, :go_after_panic),
       rule(:start_state, /http: panic serving/, :go_goroutine),
       rule(:go_after_panic, /^$/, :go_goroutine),
       rule([:go_after_panic, :go_after_signal, :go_frame_1],

test/plugin/test_exception_detector.rb

@@ -262,6 +262,30 @@ class ExceptionDetectorTest < Test::Unit::TestCase
 created by net/http.(*Server).Serve
 	/usr/local/go/src/net/http/server.go:2851 +0x2f5
 END
+
+  GO_RECOVERED = <<END.freeze
+panic: foo [recovered]
+	panic: foo [recovered]
+	panic: foo [recovered]
+	panic: foo
+
+goroutine 1 [running]:
+main.recoverAndPanic()
+	/tmp/sandbox1820875720/prog.go:12 +0x34
+panic({0x459120, 0x476600})
+	/usr/local/go-faketime/src/runtime/panic.go:838 +0x207
+main.recoverAndPanic()
+	/tmp/sandbox1820875720/prog.go:12 +0x34
+panic({0x459120, 0x476600})
+	/usr/local/go-faketime/src/runtime/panic.go:838 +0x207
+main.recoverAndPanic()
+	/tmp/sandbox1820875720/prog.go:12 +0x34
+panic({0x459120, 0x476600})
+	/usr/local/go-faketime/src/runtime/panic.go:838 +0x207
+main.main()
+	/tmp/sandbox1820875720/prog.go:7 +0x5d
+END
+
   CSHARP_EXC = <<END.freeze
 System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.
   at System.Collections.Generic.Dictionary`2[System.String,System.Collections.Generic.Dictionary`2[System.Int32,System.Double]].get_Item (System.String key) [0x00000] in <filename unknown>:0
@@ -635,6 +659,7 @@ def test_go
     check_exception(GO_ON_GAE_EXC, false)
     check_exception(GO_SIGNAL_EXC, false)
     check_exception(GO_HTTP, false)
+    check_exception(GO_RECOVERED, false)
   end
 
   def test_ruby