[Rust] Update rust install in dockerfile (#1855)

* Update rust docker

* minor edit for consistency

docker/Dockerfile.ci_cpu

@@ -30,6 +30,7 @@ RUN bash /install/ubuntu_install_rust.sh
 # SGX deps
 COPY install/ubuntu_install_sgx.sh /install/ubuntu_install_sgx.sh
 RUN bash /install/ubuntu_install_sgx.sh
+ENV LD_LIBRARY_PATH /opt/sgxsdk/lib64:${LD_LIBRARY_PATH}
 
 
 ENV PATH $PATH:/root/.cargo/bin:/usr/lib/go-1.10/bin

docker/install/ubuntu_install_rust.sh

@@ -4,6 +4,7 @@ curl -sSo rustup.sh 'https://sh.rustup.rs'
 # rustc nightly-2018-08-25 is the version supported by the above version of rust-sgx-sdk
 bash rustup.sh -y --no-modify-path --default-toolchain nightly-2018-08-25
 . $HOME/.cargo/env
+rustup toolchain add nightly
 rustup component add rust-src
-cargo install rustfmt-nightly --force
-cargo install xargo
+cargo +nightly install rustfmt-nightly --version 0.99.5 --force
+cargo +nightly install xargo