I managed to convert the Vodacom P8 Lite from single sim to dual sim (build number ALE-L21C02B130 to ALE-L21V100R001C432B046b).
Follow the instructions from post #1 in this link:
http://forum.xda-developers.com/p8lite/help/stock-rom-huawei-p8-lite-t3125331
1. Download the firmware from the "mega.co.nz" link in the above xda link.
2. Read the instructions included in the archive which you have downloaded (Word file).
3. Follow steps 1 and 2, and then do step 1 again.
I downloaded the file from the mega.co.nz link with a laptop and then transferred the files to an SD card before each step and then inserted into the phone (repeated 3 times).
After this it is working perfectly with dual sims.