bitcoin-cli importprivkey to the same user or different users
You can set account like that

bitcoin-cli importprivkey "myPrivKey" "Account" true


if you want to import multi private keys do it like that

bitcoin-cli importprivkey "myPrivKey" "Account" false
bitcoin-cli importprivkey "myPrivKey" "Account" false
bitcoin-cli importprivkey "myPrivKey" "Account" false
bitcoin-cli importprivkey "myPrivKey" "Account" true


So you don't rescan the entire local block database each time, but the last time.

to import it to default account leave it empty 

bitcoin-cli importprivkey "myPrivKey" "" true


Also please consider stopping using accounts since it will be removed in 0.16 version.