cbench can't be installed via luarocks

[Konstantin Nazarov]

$ luarocks install cbench

Installing http://rocks.tarantool.org/cbench-scm-1.rockspec...
Using http://rocks.tarantool.org/cbench-scm-1.rockspec... switching to 'build' mode

Error: Could not find header file for MSGPUCK
  No file msgpuck/msgpuck.h in /usr/local/include
  No file msgpuck/msgpuck.h in /usr/include
You may have to install MSGPUCK in your system and/or pass MSGPUCK_DIR or MSGPUCK_INCDIR to the luarocks command.
Example: luarocks install cbench MSGPUCK_DIR=/usr/local

The reason is that msgpuck.h header doesn't have msgpuck/ prefix. On both centos and alpine it's located in:
/usr/local/include/msgpuck.h

[Konstantin Nazarov]

@rtsisyk please review