Fix incorrect handling of snprintf return value.

The code assumed that snprintf would never return a value less than
the passed in size of the buffer. This is not accurate, so fix all
of the places this assumptions is made. Also, if the name is too large,
then truncate just the name to make everything fit.

Added a new set of tests for this code. Verified that the old code passes
on the _normal and _exact version of the tests, but fails with the
FORTIFY error on the _truncated version of the tests. All tests pass
on the new code.

Bug: 27324359

(cherry picked from commit 626efb78)

Change-Id: Iba60a926cf5a1d6b517a6bfd8c797d724f093010