Bootstrap script should be idempotent

[gortok]

The Bootstrap script (bootstrap.sh) should be able to be run multiple times without adverse side effects. As pointed out in the README.md in #46, running it twice results in multiple KVPs being insert into the same keys/mc.json file.

Here's the offending lines:

touch keys/mc.json
echo -e "{\n\t\"apiKey\":\"\"\n}" >> ./keys/mc.json

Proposed fix would be to add an if block around the echo and ensure that file is empty.