common: log when we toggle IO logging, don't edit env in tests!

Tests were failing when in the same thread after a test which set
log_all_io=True, because SIGUSR1 seemed to be turning logging *off*.

This is due to Python using references not copies for assignment.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tests/utils.py

@@ -81,7 +81,7 @@ class TailableProc(object):
     def __init__(self, outputDir=None, verbose=True):
         self.logs = []
         self.logs_cond = threading.Condition(threading.RLock())
-        self.env = os.environ
+        self.env = os.environ.copy()
         self.running = False
         self.proc = None
         self.outputDir = outputDir