make test: Fix too wide subprocess exceptions

When a command fails, CalledProcessError is raised. testing with except: masks other failures.

Change-Id: I7e3a6739411cb6a4c13e96dd123aff9159213fea
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>

test/framework.py

@@ -348,7 +348,7 @@ class VppTestCase(unittest.TestCase):
                                        stdout=subprocess.PIPE,
                                        stderr=subprocess.PIPE,
                                        bufsize=1)
-        except Exception as e:
+        except subprocess.CalledProcessError as e:
             cls.logger.critical("Couldn't start vpp: %s" % e)
             raise