CI Improvements (#2928)

* Switch to Windows 2019

* use macOS 10.14 and do not install Rust when not not necessary, fix rust_flags

.ci/install.yml

@@ -1,21 +1,16 @@
 steps:
   - script: |
-      curl -sSf -o rustup-init.exe https://win.rustup.rs
-      rustup-init.exe -y
-      echo "##vso[task.setvariable variable=PATH;]%PATH%;%USERPROFILE%\.cargo\bin"
       git apply .ci/win.patch
       choco install -y llvm
-    displayName: Windows Install Rust
+    displayName: Windows Install LLVM
     condition: eq( variables['Agent.OS'], 'Windows_NT' )
   - script: |
       curl https://sh.rustup.rs -sSf | sh -s -- -y
       echo "##vso[task.setvariable variable=PATH;]$PATH:$HOME/.cargo/bin"
     displayName: macOS Install Rust
     condition: eq( variables['Agent.OS'], 'Darwin' )
   - script: |
-      curl https://sh.rustup.rs -sSf | sh -s -- -y
       sudo apt-get update -yqq
       sudo apt-get install -yqq --no-install-recommends libncursesw5-dev
-      echo "##vso[task.setvariable variable=PATH;]$PATH:$HOME/.cargo/bin"
-    displayName: Linux Install Rust and Dependencies
+    displayName: Linux Install Dependencies
     condition: eq( variables['Agent.OS'], 'Linux' )

azure-pipelines.yml

@@ -26,7 +26,7 @@ pr:
 
 variables:
   RUST_BACKTRACE: '1'
-  RUST_FLAGS: '-C debug-assertions'
+  RUSTFLAGS: '-C debug-assertions'
 
 jobs:
 - job: linux
@@ -55,7 +55,7 @@ jobs:
     - template: '.ci/release.yml'
 - job: macos
   pool:
-    vmImage: macos-10.13
+    vmImage: macos-10.14
   strategy:
     matrix:
       test:
@@ -69,7 +69,7 @@ jobs:
     - template: '.ci/release.yml'
 - job: windows
   pool:
-    vmImage: vs2017-win2016
+    vmImage: windows-2019
   strategy:
     matrix:
       test: