Tolerate unknown host DCs more gracefully

For load balancing purposes, hosts are assumed to be in
the local datacenter now if the actual datacenter is unknown.

However, this is still a slight problem with contact points
in a remote DC when using DCAwareRoundRobinPolicy. See
https://datastax-oss.atlassian.net/browse/JAVA-138 for
more details.

Fixes #5
import from concurrent.futures rather than futures to prevent annoying DeprecationWarning
Merge pull request #6 from daubman/import_concurrent_futures_to_prevent_DeprecationWarning

import from concurrent.futures rather than futures to prevent annoying warning
Fix token metadata test integration with CCM
Fix failing up/down handling integration test
Don't log to stdout by default on integration tests
Avoid race in schema refresh integration test
Fix bad interpretation of prepared stmt ID spec

There is actually only one query ID associated with each
prepared statement, and it is written as a short_string.  That is,
it's a short length followed by a string.  This was misinterpreted
as a short ID and a 16 byte md5 id.
Skip libev tests if pyev fails to import
Avoid race condition around event loop stop and restart
Log ControlConnection errors at DEBUG
Minimize extra schema agreement checks
Clarify libev version and pyev workaround
Merge pull request #8 from joaquincasares/update_dep_instructions

Clarify libev version and pyev workaround
Add scales to install_requires
Basic Metrics class initialization
Documentation for metrics attributes
Add a request_timer attribute to Metrics
Add methods for incrementing counters
Hook into metrics when enabled