Prevent macOS Sierra from prompting for the password for other encrypted volume
You can edit /etc/fstab if you don't want a partition to mount on startup. I haven't tried personally but there's a writeup at Mac OS X Hints.

In short, get the UUID of the partition and add something like:

UUID=F0E430C1-5558-3BB3-9FA9-6904B663FEEA  none  hfs  rw,noauto