Adding auto-retry mechanism when connnection fails to cassandra.

  NOTE: This will retry 10x before giving up.

  Credit to @pezra also for pairing.
Added :max_retries configuration parameter for customization of maximum retries that will be made to reconnect to cassandra

  * Added spec stubs
  * Modified template for config file (added max-retries)
Adding specs for max retries in Cequel::Metal::Keyspace#execute
Changing default max-retries to 3
Defining clearer spec for failed connection testing in Cequel::Metal::Keyspace
Changing default max-retries to 3 in `cequel.yml` template and documentation
Changed `max-retries` to `max_retries` and using ` clear_active_connections!` instead of directly accessing ivar
Removing unnecessary exception variable and quotes around symbol
Merge pull request #133 from alakra/add_auto_retry_mechanism_on_connection_failure

Add auto retry mechanism on connection failure