nsfarm/mterm: suppress logging

It is common that tests are run with logs printed to terminal. It helps
developer to see what is actually happening.
The problem is that log printing interferes with terminal output. It
should be safe to set level of root logger such it prints no messages
for time of mterm execution.

nsfarm/mterm.py

@@ -6,6 +6,7 @@ import sys
 import fcntl
 import select
 import termios
+import logging
 import warnings
 
 
@@ -30,6 +31,8 @@ def mterm(fileno: int):
     if not sys.stdin.isatty():
         warnings.warn("Microterm works only if stdin is directly the terminal.", RuntimeWarning)
         return
+    prev_log_level = logging.getLogger().getEffectiveLevel()
+    logging.getLogger().setLevel(logging.CRITICAL)
     orig_tio = termios.tcgetattr(sys.stdin)
     orig_filestatus = fcntl.fcntl(fileno, fcntl.F_GETFL)
     print("--- Microterm (use ^] to exit) ---", file=sys.stderr)
@@ -55,4 +58,5 @@ def mterm(fileno: int):
     finally:
         termios.tcsetattr(sys.stdin, termios.TCSANOW, orig_tio)
         fcntl.fcntl(fileno, fcntl.F_SETFL, orig_filestatus)
+        logging.getLogger().setLevel(prev_log_level)
         print("\n--- Microterm exit ---", file=sys.stderr)