Reinstalling toolchains with rustup does not preserve components/targets

[ajungren]

When rustup install attempts to update a toolchain but fails, the toolchain is uninstalled and reinstalled. The issue is that none of the components or targets are reinstalled after the toolchain is. Not reinstalling the same targets isn't ideal but as long as every build uses the cargo runner in TeamCity the target will be added on the next build, test, etc. Not reinstalling the components, however, requires manual intervention if rustfmt (also cargo fmt) and/or clippy (also cargo clippy) are used because these aren't supported by this plugin (#44) so they won't be reinstalled.

Ideally, reinstalling the toolchain would be optional and fail the build if the toolchain couldn't be updated and reinstallation is disabled, but reinstalling the components that were previously installed would at least stop it from breaking builds until they're manually reinstalled.