Provide Jenkins slave image for Rust

Summary:
The current validation use case is to build and publish
Limiting Factor (rLF) documentation.

Fixes T1406.

Test Plan:

$ su - app
$ git clone https://devcentral.nasqueron.org/source/limiting-factor.git
$ cd limiting-factor
$ cargo build
$ cargo doc
# Fails with Diesel build, like on workstation
$ cargo doc --no-deps
# Documentation is at target/doc

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1406

Differential Revision: http://devcentral.nasqueron.org/D1744