Can I get the wallet in bitcoind to use P2SH segwit (on testnet)? Can I use the wallet functionality in bitcoin cli daemon with P2SH segwit on testnet/regtest? Meaning, can I receive on these addresses and send from them?

And if I can, how? 

I cannot find it anywhere in the help. The only one that gets close is addwitnessaddress, but that does something else, too.
addwitnessaddress is what you want

create it, fund it and spend coins from it - then check your transactions on any blockexplorer that they are in segwit format