tools: add a script that updates bootstrap.snap

By design after patching update.lua, introducing new data version,
a developer needs to update bootstrap.snap, which would have the
new data version.

Generation of bootstrap.snap is a bit tricky, there's a manual:
https://github.com/tarantool/tarantool/wiki/How-to-generate-new-bootstrap-snapshot

This commit presents a simple script that automates the process.
Just run it in tarantool build directory and check its output.
Check --help for script options.

Follow-up of tarantool/security#14

NO_DOC=internal tool
NO_TEST=internal tool
NO_CHANGELOG=internal tool

(cherry picked from commit 0922816e)