[MERGE][#299313] --local commits are accessing the network

[Vincent Ladeuil]

I didn't follow closely how we end up changing the default
behavior of branch.nick *but* please take into account that it
'breaks' the test suite when run in a bound branch.

One of the reasons is that some tests use 'bzr --version' as a
'do very little' command and, when the bound branch requires some
password (like any ssh one does)... selftest prompts and hangs..

I use an ssh agent but the test suite (rightly) reset the
SSH_AUTH_SOCK.

bzr selftest -s bb.test_selftest.TestRunBzrSubprocess.test_run_bzr_subprocess

is one such test.

      Vincent