Update defaults logic for multi-pem

[1000TurquoisePogs]

This PR fixes zowe/zlux#976 by updating the defaults to handle 3 different cases in the pem CA section:

1. if the section is an array, return it without wrapping in an array (was a bug, ended up with 2 arrays)
2. if the section isnt an array, its a string which may be many entries if it has a ,. so, do a split(,), which even if there's just 1 entry you still get an array.

[DivergentEuropeans]

This makes sense