cli.py: Add a CLI option disabling log record prints

Try to spend the least amount of time handling logging in gRPC thread
executors: do not log to standard output and standard error channels if
'--no-print' is specified (for use in production).

buildgrid/_app/cli.py

@@ -27,6 +27,7 @@ import os
 import click
 import grpc
 
+from buildgrid.settings import LOG_RECORD_FORMAT
 from buildgrid.utils import read_file
 
 CONTEXT_SETTINGS = dict(auto_envvar_prefix='BUILDGRID')
@@ -139,10 +140,12 @@ class BuildGridCLI(click.MultiCommand):
 
 
 @click.command(cls=BuildGridCLI, context_settings=CONTEXT_SETTINGS)
+@click.option('--no-print', is_flag=True, show_default=True,
+              help="Do not print log records to stdout/stderr.")
 @click.option('-v', '--verbose', count=True,
               help='Increase log verbosity level.')
 @pass_context
-def cli(context, verbose):
+def cli(context, no_print, verbose):
     """BuildGrid App"""
     logger = logging.getLogger()
 
@@ -152,14 +155,15 @@ def cli(context, verbose):
     for log_filter in logger.filters[:]:
         logger.removeFilter(log_filter)
 
-    logging.basicConfig(
-        format='%(asctime)s:%(name)32.32s][%(levelname)5.5s]: %(message)s')
-
+    # Do not register a stream handler if no-print is requested:
+    if not no_print:
+        logging.basicConfig(format=LOG_RECORD_FORMAT)
+    else:
+        logging.basicConfig(format=LOG_RECORD_FORMAT,
+                            handlers=[logging.NullHandler()])
     if verbose == 1:
         logger.setLevel(logging.WARNING)
     elif verbose == 2:
         logger.setLevel(logging.INFO)
     elif verbose >= 3:
         logger.setLevel(logging.DEBUG)
-    else:
-        logger.setLevel(logging.ERROR)