Fix for config.session being ignored

[juancampa]

Problem

config.session was being ignored after #3352

Solution

Don't ignore config.session and pass it to node-pty.

Diff looks a bit noisy because I renamed some variables and now I'm returning options instead of uid from create session

Tests

• Initial sessions use the right shell
• subsequent sessions use the right shell

[Stanzilla]

Can confirm this unbreaks the shell feature on Windows.