tests: support attaching to existing vpp

Introduce a new option DEBUG=attach to run a test against existing
already running vpp. A new target 'make test-start-gdb' will spawn VPP
in gdb for this purpose. Customization options explained in test-help.

Type: improvement
Change-Id: Ia160a85b33da3b2df292d44bb95729af9dd9da96
Signed-off-by: Klement Sekera <ksekera@cisco.com>
diff --git a/Makefile b/Makefile
index 78300e2..0f0af4a 100644
--- a/Makefile
+++ b/Makefile
@@ -505,6 +505,14 @@
 	$(eval EXTENDED_TESTS=yes)
 	$(call test,vpp,vpp_debug,retest)
 
+.PHONY: test-start-vpp-in-gdb
+test-start-vpp-in-gdb:
+	$(call test,vpp,vpp,start-gdb)
+
+.PHONY: test-start-vpp-debug-in-gdb
+test-start-vpp-debug-in-gdb:
+	$(call test,vpp,vpp_debug,start-gdb)
+
 ifeq ("$(wildcard $(STARTUP_CONF))","")
 define run
 	@echo "WARNING: STARTUP_CONF not defined or file doesn't exist."