Update gitlab CI script, add cpp lint

docker/Dockerfile.lint

@@ -1,6 +1,18 @@
-FROM python:2.7
+FROM esphome/esphome-base-amd64:1.5.1
 
-COPY requirements.txt /requirements.txt
+RUN \
+    apt-get update \
+    && apt-get install -y --no-install-recommends \
+        clang-format-7 \
+        clang-tidy-7 \
+        patch \
+    && rm -rf \
+        /tmp/* \
+        /var/{cache,log}/* \
+        /var/lib/apt/lists/*
 
-RUN pip install -r /requirements.txt && \
-    pip install flake8==3.6.0 pylint==1.9.4 pillow
+COPY requirements_test.txt /requirements_test.txt
+RUN pip2 install -r /requirements_test.txt
+
+VOLUME ["/esphome"]
+WORKDIR /esphome