Merge branch 'store_has_reactor' into as-170-local-lock
Weak cache of locks

Implemented weak cache of DeferredLocks mapped based on string using
weakref module. The lock is created on a string when asked. When the
lock has been utilized, it is expected to be garbage collected sometime
later.
Acquiring local lock before kazoo lock

A mapping of local locks based on group id is stored in CassScalingGroupCollection that is
used to when modifying state. First local lock is acquired, then kazoo
lock is acquired before getting and modifying state. This will reduce zk
traffic to one call per group at any point in time. So, 200+ servers can
be easily created in one execution
Merge branch 'master' into as-170-local-lock
Checking ScalingGroup.local_locks - thanks @cyli
Merge pull request #607 from rackerlabs/as-170-local-lock

AS-170 local lock