use os-swift memcache.conf to manage memcached configuration

We should support the use of a memcache.conf to manage memcached configuration for the swift cluster, because work is being added to allow services to reload this config allowing changes to memcache servers without restarting swift services.

There is a sample memcache.conf file under the etc directory of the swift source. Which contains:

  [memcache]
  # You can use this single conf file instead of having memcache_servers set in
  # several other conf files under [filter:cache] for example. You can specify
  # multiple servers separated with commas, as in: 10.1.2.3:11211,10.1.2.4:11211
  # memcache_servers = 127.0.0.1:11211
  #
  # Sets how memcache values are serialized and deserialized:
  # 0 = older, insecure pickle serialization
  # 1 = json serialization but pickles can still be read (still insecure)
  # 2 = json serialization only (secure and the default)
  # To avoid an instant full cache flush, existing installations should
  # upgrade with 0, then set to 1 and reload, then after some time (24 hours)
  # set to 2 and reload.
  # In the future, the ability to use pickle serialization will be removed.
  # memcache_serialization_support = 2
  #
  # Sets the maximum number of connections to each memcached server per worker
  # memcache_max_connections = 2
  #
  # Timeout for connection
  # connect_timeout = 0.3
  # Timeout for pooled connection
  # pool_timeout = 1.0
  # number of servers to retry on failures getting a pooled connection
  # tries = 3
  # Timeout for read and writes
  # io_timeout = 2.0

This config file just needs to be placed under /etc/swift on swift hosts that need to talk to memcache (and those that don't as it wont hurt).