Updating rebar version

Will be adding CT tests, and these run better with a newer version that
can match the fact that newer versions of CT return non-0 exit codes on
case failures
Connection failure tolerance

When the redgrid service cannot connect to the redis server, do an
incremental backoff and suspend operations up until the connection is
established.

This results in a less obvious failure mode, but will not take down a
node due to repeated failures following a netsplit or outage external to
the node. We're deciding that failing to connect is better than failing
totally as much as partial failures go.

This adds a dependency on the 'backoff' library, which tracks
exponential backoffs.
Allow configuration reloading

Configuration is static and would require to restart a redgrid service.
This patch adds a call to reload the configuration and reset the
connection, and to keep going from there.
Basic test suite for connection failures

This is a test suite that so far verifies that redgrid can connect and
disconnect from a redis node, reload its configuration, and survive
operations that rely on redis being there or otherwise fail.

The test suite *DOES NOT* test regular operations such as
publishing/fetching information from redis.
Bumping to 1.0.3