Shell out to echo instead of printing, if NSUnbufferedIO env var is set

CHANGELOG.md

@@ -40,7 +40,6 @@ All notable changes to this project will be documented in this file. This projec
 
 ### Known Issues
 - On macOS 10.14 (and possibly earlier) an incorrect "certificate has expired" warning may appear in the output. (#165)
-- Script output does not appear in the app until the script is completely done processing. I hope to restore realtime output in a later version.
 - The "jss-upload" type is not addressable yet in the Recipe Robot app, only in the script.
 - Because Recipe Robot is now using plistlib instead of FoundationPlist, it's likely that some non-standard developer plist files may not successfully parse. This is because plistlib is stricter than FoundationPlist, and the same issue applies to AutoPkg itself (see [autopkg#618](https://github.com/autopkg/autopkg/issues/618) for an example).
 

scripts/recipe_robot_lib/tools.py

@@ -183,7 +183,10 @@ def robo_print(message, log_level=LogLevel.LOG, indent=0):
             and (OutputMode.verbose_mode or OutputMode.debug_mode)
         )
     ):
-        if log_level in (LogLevel.ERROR, LogLevel.WARNING):
+        if os.environ.get("NSUnbufferedIO") == "YES":
+            # Shell out to enable realtime output in Recipe Robot app.
+            subprocess.run(["echo", line])
+        elif log_level in (LogLevel.ERROR, LogLevel.WARNING):
             print(line, file=sys.stderr)
         else:
             print(line)