Update CI scripts to use cargo bootimage

.appveyor.yml

@@ -73,4 +73,4 @@ before_test:
   - cargo install-latest cargo-xbuild bootimage
 
 test_script:
-  - bootimage build
+  - cargo bootimage

.travis.yml

@@ -30,9 +30,8 @@ cache:
 
 before_script:
   - rustup component add rust-src llvm-tools-preview
-  - (test -x $HOME/.cargo/bin/cargo-install-latest || cargo install cargo-install-latest)
+  - cargo install cargo-xbuild bootimage cargo-cache --debug -Z install-upgrade
-  - cargo install-latest cargo-xbuild bootimage cargo-cache
 
 script:
-  - bootimage build
+  - cargo bootimage
   - cargo cache --autoclean

azure-pipelines.yml

@@ -52,12 +52,10 @@ steps:
 - script: rustup component add rust-src llvm-tools-preview
   displayName: 'Install Rustup Components'
 
-- script: |
+- script: cargo install cargo-xbuild bootimage --debug
-    cargo install cargo-xbuild --debug
-    cargo install bootimage --debug
   displayName: 'Install cargo-xbuild and bootimage'
 
-- script: bootimage build
+- script: cargo bootimage
   displayName: 'Build'
 
 - script: rustup component add rustfmt