fix bug #253 "NetworkManager runs DHCP..." for Ubuntu (but not Fedora/CentOS)

use "vethA.B.SS" name for veth devices (A = node number, B = index, SS = short session ID)
use "tapA.B.SS" name for tap devices; use "b.A.SS" name for bridge devices
added a SESSION_SHORT environment variable to the default CORE environment
(Boeing r1867)

daemon/core/session.py

@@ -321,6 +321,7 @@ class Session(object):
         '''
         env = os.environ.copy()
         env['SESSION'] = "%s" % self.sessionid
+        env['SESSION_SHORT'] = "%s" % self.shortsessionid()
         env['SESSION_DIR'] = "%s" % self.sessiondir
         env['SESSION_NAME'] = "%s" % self.name
         env['SESSION_FILENAME'] = "%s" % self.filename