Support for user defined ports via DOCKER_RIAK_BASE_HTTP_PORT

The default port config is -P, which means that docker with assign
arbitrary ports for riak to use.  These are usually in the 49xxx range.

if DOCKER_RIAK_BASE_HTTP_PORT is set, then we will manually forward
port number $DOCKER_RIAK_BASE_HTTP_PORT + $index to 8098
and forward $DOCKER_RIAK_BASE_HTTP_PORT + $index + $DOCKER_RIAK_PROTO_BUF_PORT_OFFSET to 8087
DOCKER_RIAK_PROTO_BUF_PORT_OFFSET is optional and defaults to 100

example usage:

DOCKER_RIAK_BASE_HTTP_PORT=8800 DOCKER_RIAK_AUTOMATIC_CLUSTERING=1 DOCKER_RIAK_CLUSTER_SIZE=5 make start-cluster
Merge branch 'collectivehealth-develop' into develop
0.4.2
Merge branch 'release/0.4.2' into develop
Updating start/test cluster scripts to support the docker client

When DOCKER_HOST is set and docker is being used as a client, having 127.0.0.1
hard coded causes issues
Merge branch 'bfosberry-develop' into develop
0.4.3
Merge branch 'release/0.4.3' into develop
configure riak to use leveldb and to sort secondary indices