Upstream zone: store peers->name and its data in shared memory.

Upstream zone: store peers->name and its data in shared memory.

The shared objects should generally be allocated from shared memory.
While peers->name and the data it points to allocated from cf->pool
happened to work on UNIX, it broke on Windows.  On UNIX this worked
only because the shared memory zone for upstreams is re-created for
every new configuration.

But on Windows, a worker process does not inherit the address space
of the master process, so the peers->name pointed to data allocated
from cf->pool by the master process, and was invalid.