With the new version of mbed, you always get the following error:

[mbed] Auto-installing missing Python modules...
[mbed] WARNING: Unable to auto-install required Python modules.
       The mbed OS tools in this program require the following Python modules: git
       You can install all missing modules by running "pip install -r requirements.txt" in "/home/jim/AvNet/mbed-os-example-wifi/mbed-os"
       On Posix systems (Linux, Mac, etc) you might have to switch to superuser account or use "sudo"

I know those modules have been installed because i did a:
sudo -H pip install -r requirements.txt
and it reported that is was successfully installed prior to issuing the:
mbed add esp8266-driver
command. In spite of that, I always get the same error when compiling or adding libraries. It seems like the mbed command isn't working correctly for some reason. Even though that error/warning is displayed, everything appears to work correctly.