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/test/sanity_run_vpp.py b/test/sanity_run_vpp.py
index 5eb6885..f91dc83 100644
--- a/test/sanity_run_vpp.py
+++ b/test/sanity_run_vpp.py
@@ -43,8 +43,8 @@
     y.close()
 
     if rc == 0:
-        print('Sanity test case passed.\n')
+        print('Sanity test case passed.')
     else:
-        print('Sanity test case failed.\n')
+        print('Sanity test case failed.')
 
     sys.exit(rc)