Default GAME env var to KSP in Inflator Dockerfile, fix redeploy

[HebaruSan]

Problem

If the $GAME environment variable isn't set, the Inflator won't start, as of #3797.

Also the docker-inflator Cake build target tries to redeploy the Inflator container, but that was renamed to InflatorKsp in KSP-CKAN/NetKAN-Infra#284. And the InflatorKsp2 container isn't touched at all.

Changes

• Now if it's not set, we fall back to a default value of KSP using bash's ${ENVVAR:-defaultval} syntax.
  • https://stackoverflow.com/questions/2013547/assigning-default-values-to-shell-variables-with-a-single-command-in-bash
• Now we redeploy InflatorKsp followed by InflatorKsp2

[techman83]

LGTM! Thanks!