I needed to place some files in system/etc and no method of remounting as read-write was allowing me to write into the read-only system folder. It took me forever to find a solution so just wanted to place this as a separate question so that people don't have to go through that exercise. The answer was found here: https://stackoverflow.com/a/42280124/10844761 many thanks to ishamael
and here's the summary:
you need to open the emulator with -writable-system
go to /path/to/andorid/sdk/emulator and run ./emulator -writable-system avd name-of-your-device-emulator
if you don't know the name of your device emulator run ./emulator -list-avds
now once the emulator starts up run adb root adb remount
now you can write to system folder :)
