MB-37096: cluster_test: use getpid() on Windows for parent_identifier
MB-37096: cluster_test: use getpid() on Windows for parent_identifier

Previously cluster_test used GetCurrentProcess() to obtain the process
identifier for the parent process of each memcached; so they terminate
if the test terminates.

However, GetCurrentProcess() returns a pseudo ID - '-1' which is not
useful from the context of another process.

Instead just use getpid() which works on Windows.

Change-Id: I64a856bb4bd0ddee74f812e6f9fd331c72acb35b
Reviewed-on: http://review.couchbase.org/121488
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Paolo Cocchi <9dd88c9f3e5cbab6e19a6c020f107e0c648ac956@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine