cloudfabric: only install firewall if firewall in use

GDB-671 #resolve
cloudfabric: only disable selinux if selinux in use

GDB-672 #resolve
Debian: dependency on python-unittest2

GDB-674 #resolve

This is needed for the tests module, but must be installed even if the
tests aren't being run.

We must install python-unittest2 even if python2.7 is the default python,
as the module could be loaded from a script ran under python2.6. Only when
the target debian distribution *only* has pythons with unittest2 build in
can we forgo depending on it.