The strncpy() function has this quirk where it will copy
*up* to the requested number of bytes, that is, it will
stop early if it encounters a NULL byte in the source
string.

This makes it legal to pass the size of the destination
buffer (minus one byte needed for the string terminator)
as the number of bytes to copy and still get something
somewhat reasonable out of the operation; unfortunately,
it also makes the function difficult to reason about
and way too easy to misuse.

We want to move away from the way strncpy() behaves and
towards better defined semantics, where virStrncpy()
will always copy *exactly* the number of bytes it's
been asked to copy; before we can do that, though, we
have to change a few of the callers.
Signed-off-by: NAndrea Bolognani <abologna@redhat.com>