Don't construct Context as a global variable
Don't construct Context as a global variable

Constructing context as a global variable in ClusterPerf makes the
order of construction and destruction uncontrollable. Especially this
caused problem with new LogProtector mechanism. LogProtector's global
epochProviers list sometimes destructed before destruction of context
(context's destructor chain eventually destroys ServerRpcPool.) and
causes segfault.
* Now context is a local variable of main().
RAM-812 #close LogProtector was not buggy. LogCleaner is fine.

anirajk/RAMCloud,utah-scs/RAMCloud,SMatsushi/RAMCloud,jblomer/ramcloud,anirajk/RAMCloud,utah-scs/RAMCloud,SMatsushi/RAMCloud,SMatsushi/RAMCloud,SMatsushi/RAMCloud,jblomer/ramcloud,anirajk/RAMCloud,utah-scs/RAMCloud,SMatsushi/RAMCloud,jblomer/ramcloud,jblomer/ramcloud,SMatsushi/RAMCloud,anirajk/RAMCloud,anirajk/RAMCloud,utah-scs/RAMCloud,anirajk/RAMCloud,utah-scs/RAMCloud,jblomer/ramcloud,utah-scs/RAMCloud,jblomer/ramcloud