tests: refactor VppDiedError.

- Move Exception into same module as TestCase.
- Move the error reporting logic inside the error.
- Allows testing of the returncode and signal_name for tests to consume.
- Fix the signal reporting code:
	VppDiedError: VPP subprocess died unexpectedly with returncode -6 [unknown].
    displays as:
	VppDiedError: VPP subprocess died unexpectedly with return code: -6 [SIGABRT].

Type: test

Change-Id: I8488ab318a596c9b737308829cedfb7e96e57302
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 1943c0f..bb62ca3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -332,7 +332,11 @@
 F:	src/plugins/nsim/
 
 Test Infrastructure
+<<<<<<< HEAD
 I:  tests
+=======
+I:	tests
+>>>>>>> d84661c... tests: refactor VppDiedError.
 M:	Klement Sekera <ksekera@cisco.com>
 M:	Paul Vinciguerra <pvinci@vinciconsulting.com>
 F:	test/