Fix: logging: possible buffer overflows

Fix: logging: possible buffer overflows

Issue
=====
Multiple possible buffer overflows on string operations using the
`SET_TMP_PREFIX()` macro that uses `strcpy()` on parameter char array.

Solution
========
Use a #define to set the length of the destination array and use it as
the size parameter of the `strncpy()` and `strncat()` calls.

Drawbacks
=========
None.

Notes
=====

Coverity reported defects:
  CID 1401179 (#5 of 5): Copy into fixed size buffer (STRING_OVERFLOW) 9.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401181 (#1 of 1): Copy into fixed size buffer (STRING_OVERFLOW) 5.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length

  CID 1401186 (#1 of 1): Copy into fixed size buffer (STRING_OVERFLOW) 15.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401192 (#2 of 2): Copy into fixed size buffer (STRING_OVERFLOW) 4.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401197 (#1 of 1): Copy into fixed size buffer (STRING_OVERFLOW) 6.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401198 (#4 of 4): Copy into fixed size buffer (STRING_OVERFLOW) 15.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401203 (#1 of 1): Copy into fixed size buffer (STRING_OVERFLOW) 28.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401212 (#1 of 1): Copy into fixed size buffer (STRING_OVERFLOW) 12.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401215 (#4 of 4): Copy into fixed size buffer (STRING_OVERFLOW) 16.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401221 (#2 of 2): Copy into fixed size buffer (STRING_OVERFLOW) 19.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401227 (#1 of 1): Copy into fixed size buffer (STRING_OVERFLOW) 13.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401230 (#3 of 3): Copy into fixed size buffer (STRING_OVERFLOW) 10.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401232 (#3 of 3): Copy into fixed size buffer (STRING_OVERFLOW) 23.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401234 (#5 of 5): Copy into fixed size buffer (STRING_OVERFLOW) 19.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401254 (#10 of 10): Copy into fixed size buffer (STRING_OVERFLOW) 10.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401257 (#1 of 1): Copy into fixed size buffer (STRING_OVERFLOW) 9.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

  CID 1401261 (#2 of 2): Copy into fixed size buffer (STRING_OVERFLOW) 11.
  fixed_size_dest: You might overrun the 64-character fixed-size string
  tmp_prefix by copying prefix without checking the length.

Reported-by: Coverity - Copy into fixed size buffer (STRING_OVERFLOW)
Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I922f1fb82a95e06b0c42627a2e57ba94debe1c5a
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1329
Reviewed-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Tested-by: jenkins