Fedora 28: Fix misc bounds check compiler warnings
Fix a bunch of (mostly) sprintf/snprintf truncation compiler
warnings that show up on Fedora 28 (GCC 8.0.1).
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #7361
Closes #7368