Docker image updates for integration tests. (#26054)

* Sort packages to install.
* Add python-argparse to centos6 docker image.
* Add gcc and python dev lib to docker images.
* Add python cryptography to docker images.
* Add coverage using pip instead of OS packages.
* Update old pip versions in docker images.
* Exclude */pyshared/* from coverage reporting.

.coveragerc

@@ -21,4 +21,5 @@ omit =
     */python*/dist-packages/*
     */python*/site-packages/*
     */python*/distutils/*
+    */pyshared/*
     */pytest