mysql: allow specifying connect,read,write timeouts
mysql: allow specifying connect,read,write timeouts

The Mysql driver allows these timeouts to be specified,
so allow the following parameters to be passed to the
initializer:

  :connect_timeout
  :read_timeout
  :write_timeout

These must be integer values (representing seconds)
and will be passed straight through to the underlying
Mysql driver (which will hopefully support sub-second
timeouts at some point...).

All timeouts will default to 1 (second) here.

godfat/not-used-mogilefs-client,drasch/mogilefs-client,songkick/mogilefs-client