vty_test_runner.py: raise exception when MSC socket connection fails

Instead of below error, raise an exception to describe what's happening.

Seen in a jenkins run on https://gerrit.osmocom.org/#/c/945/2:

ERROR: testBSCreload (__main__.TestVTYNAT)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "./vty_test_runner.py", line 787, in testBSCreload
    msc = nat_msc_test(self, ip, port)
  File "./vty_test_runner.py", line 1251, in nat_msc_test
    return conn
UnboundLocalError: local variable 'conn' referenced before assignment

Change-Id: Iae26e7345267a21aed0b108b089453832889c9fa
1 file changed
tree: d47095a98a072195f8719692a2fc383ca1617fd6
  1. contrib/
  2. debian/
  3. openbsc/
  4. .gitignore
  5. .gitreview
  6. .mailmap