Test: Fix `splice_utils` test when `/proc/sys/fs/pipe-max-size` is missing
Test: Fix `splice_utils` test when `/proc/sys/fs/pipe-max-size` is missing

On older systems (RHEL6), this procfs entry is missing. Whilst the code
in `splice_utils` handles this gracefully, the tests fail.

This commit adjusts the test code to handle this case correctly.

(cherry picked from commit fa8fcac43fc243e6ec93914b6da585f8c3373f2a)
Signed-off-by: Nicolas Trangez <abbeee14574502be75498298fab55c152b9bac47@nicolast.be>

scality/ScalitySproxydSwift,scality/ScalitySproxydSwift