Bug 1254313 - Log less when running mach run --debug within emacs. r=gps

Check if the INSIDE_EMACS environment variable is set and change the
log level to WARNING to not confuse the emacs/mi with logging messages.

MozReview-Commit-ID: 5AWZ6swGJsE

--HG--
extra : transplant_source : b%24%8Ff6%968%8A%02%E2%07%DD%C6Y9E%CB%7C.%E4

python/mozbuild/mozbuild/mach_commands.py

@@ -1173,6 +1173,9 @@ class RunProgram(MachCommandBase):
         extra_env = {'MOZ_CRASHREPORTER_DISABLE': '1'}
 
         if debug or debugger or debugparams:
+            if 'INSIDE_EMACS' in os.environ:
+                self.log_manager.terminal_handler.setLevel(logging.WARNING)
+
             import mozdebug
             if not debugger:
                 # No debugger name was provided. Look for the default ones on