LINT: add clang-tidy step (#6295)

* Implement new travis clang-tidy build step

* This step enable some rules and enforce one rule as error
* This permits to have some C++ quality rules based on clang & clang contributor guidelines

* Fix clang-tidy reported problems on push_back -> emplace_back

.travis.yml

@@ -96,6 +96,15 @@ matrix:
           packages: ['clang-format-5.0']
           sources: &sources
             - llvm-toolchain-trusty-5.0
+    - env: CLANG_TIDY=1
+      compiler: clang
+      os: linux
+      script: ./util/travis/clangtidy.sh
+      addons:
+        apt:
+          packages: ['clang-tidy-5.0']
+          sources: &sources
+            - llvm-toolchain-trusty-5.0