CI improvement: consider making cli usable for local use of docker

[pyramation]

This could reduce time needed in travis!

like they do here:
https://github.com/sqitchers/docker-sqitch

docker pull sqitch/sqitch
curl -L https://git.io/fAX6Z -o sqitch && chmod +x sqitch
./sqitch help

The https://git.io/fAX6Z link is actually this:
https://raw.githubusercontent.com/sqitchers/docker-sqitch/master/docker-sqitch.sh

[pyramation]

works locally! I've verified by deploying something, e.g., path/to/sqitch.sh deploy db:pg:abcdef-db

[theory]

Updated sqitch shell script URL is https://git.io/JJKCn (replace fAX6Z with JJKCn).

[pyramation]

@theory thank you! Btw, sorry I haven't yet finished those images, will be getting on it soon!