Adding support for pouchdb-server to perf tests

Set number of pouch clients in config/perf.js.  Instances will be
started up similar to current liteserv clients using non-conflicting ports.
by default internal leveldb files are stored into tmp dir.
fixes to client provisioning

we were calling t.end() before all of the clients could start
also pouchdb doesn't return session_id like liteservs
cleaner pouchdb-server startup

remove depends on lauch shell script.  initially I thought this was
necessary to start from different directories but now realizing
I can change working directory with process module
pouchdb-server should be forked

process object is global and changing dir for one instance
changes them for all which causes things like create-db to fail.
so starting each instance now in forked process