Detect NVLink info properly

Record which GPUs are connected to which via nvlinks.
Determine if each nvlink is single, double, no connect, or self.
Create device index to PCI bus id lookup table.
Fix test 39.18 by reverting parsable prints to always use info().
Add better valgrind support for test 39.18.
Update comments and remove whitespace.

We want the print statements meant for the regression tests to print
out everytime, even if user does not specify debug level.

Bug 5402