Add MacOS manual DNS patch and revert

[joaufi]

Description

• Removed the hard-coded skip_dns_patch = True to allow manual patching of /etc/resolv.conf on Mac OS (darwin)
• Original /etc/resolv.conf is moved to /etc/resolv.conf.backup before overwrite
• Added script that is called as final step before shutting down that uses the backup file to overwrite the patched /etc/resolv.conf file; backup file is removed in this process (mv -f)
• Added requirements.txt file for local development / IDE help e.g. pip install -r requirements.txt

Testing

• Ran locally on Mac OS Catalina version 10.15.1 and observed:
  1. /etc/resolv.conf being overwritten with values from manual-dns-patch.sh after original conf file is moved to /etc/resolv.conf.backup
  2. On SystemExit (using KeyboardInterrupt) observed /etc/resolv.conf.backup being used to overwrite /etc/resolv.conf
  3. Checked values before / after and they are accurate

Note

Running the subprocess as the final step before exiting seems pretty sloppy but this is currently just a hacky fix. If openpyn is force killed or quits in a way that doesn't allow it to shutdown gracefully then /etc/resolv.conf will be replaced on next system restart (Mac OS automatic process from my understanding). The /etc/resolv.conf.backup file will hang around though. 🤔

[jotyGill]

Hi joaufi,
Thanks for the pull.

First I'll have to merge the other quite big pull. I'll piggyback merge this later.
As openpyn needs to be installed at the os level (not using --user). I don't want to specify the versions of dependencies, it could lead to breakage of other stuff. besides to develop you only need to install it using -e .

git clone https://github.com/jotyGill/openpyn-nordvpn.git
cd openpyn-nordvpn
git checkout test
sudo python3 -m pip install -e .
I should mention this somewhere..
So if you could just remove requirements.txt that would be good.