Fix memtier benchmark

[ligurio]

there is a memtier benchmark added in commit a3e2815:

sergeyb@pony:~/sources/MRG/memcached$ ls -la test/bench/
total 1112
drwxrwxr-x  2 sergeyb sergeyb    4096 дек  1 19:03 .
drwxrwxr-x 11 sergeyb sergeyb    4096 дек  1 18:58 ..
-rw-r--r--  1 sergeyb sergeyb    1948 дек  1 14:14 00000000000000000000.snap
-rw-rw-r--  1 sergeyb sergeyb       0 ноя 30 16:29 .gitignore
-rw-rw-r--  1 sergeyb sergeyb     335 дек  1 19:03 memcached.lua
-rwxrwxr-x  1 sergeyb sergeyb 1106496 дек  1 14:19 memtier_benchmark
-rw-rw-r--  1 sergeyb sergeyb    8309 ноя 30 16:29 README.md
sergeyb@pony:~/sources/MRG/memcached$ 

However, it is not possible to run benchmark automatically. Need to fix it and integrate to CI.