Provide a way to install the Rust the Oasis CLI needs with the install script

[omitar]

It looks like if Rust is already installed on the system, the install script does not install anything Rust related. Which means that if the version on the system does not match what Oasis needs, you get an error like:

error: toolchain 'nightly-2019-08-01-x86_64-unknown-linux-gnu' is not installed

I suggest that or Oasis installs everything necessary even in this case (unless --no-rust is provided), or that a new switch is added, something like --force-rust, to force Rust installation with all correct versions of dependencies.

[omitar]

Even running rustup toolchain install nightly-2019-08-01-x86_64-unknown-linux-gnu is not enough. Now I am getting:

error[E0463]: can't find crate for `core`
  |
  = note: the `wasm32-wasi` target may not be installed

And rustup target install wasm32-wasi does not fix it. Installation script could really do this for me. I had to do rustup target install wasm32-wasi --toolchain nightly-2019-08-01-x86_64-unknown-linux-gnu.

[nhynes]

Wrong repo.

[nhynes]

this has been resolved