base: Add Python package check

pip install command does not return a non-zero exit code when there
exists a dependency conflict.

This commit adds a `pip3 check` call, which validates all installed
package dependencies and returns a non-zero exit code when there is a
breakage.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

Dockerfile.base

@@ -114,7 +114,8 @@ RUN python3 -m pip install -U pip && \
  -r https://raw.githubusercontent.com/zephyrproject-rtos/zephyr/master/scripts/requirements.txt \
  -r https://raw.githubusercontent.com/zephyrproject-rtos/mcuboot/master/scripts/requirements.txt \
  awscli GitPython imgtool junitparser numpy protobuf PyGithub \
- pylint sh statistics west
+ pylint sh statistics west && \
+ pip3 check
 
 # Clean up stale packages
 RUN apt-get clean -y && \