Call `zesInit()` instead of setting `ZES_ENABLE_SYSMAN` from a constructor function

[al45tair]

It looks like hwloc changes the environment from a constructor function; this seems unpleasant — it means that very likely the first thing your program will do is allocate memory and copy the environment.

Setting ZES_ENABLE_SYSMAN=1 explicitly as a workaround will stop this behaviour, but it would be better if hwloc called zesInit(0) rather than changing the environment.