docker: Elasticsearch catchup

• BETTER Adds Elasticsearch container and adds configuration for Elasticsearch search hosts called ES_HOSTS.

• Adds invenio-records as a requirement.

• Disables some tests which are using httpretty. The monkey patching used by this library leads to failures in some cases, which are difficult to reproduce. It mostly seems to affect the connection handling (which makes valid assumptions about how sockets work) of elasticsearch. An upgrade of httpretty did not lead to a fix. We might want to change to a more stable HTTP mocking system.

• BETTER Improves parts of the Docker documentation.

• INCOMPATIBLE Upgrades the general requests library minimal requirement in Invenio to version 2.4. This will lead to the usage of keep-alive in most cases. Elasticsearch uses this to improve efficiency.

• INCOMPATIBLE Switches from hard-coded Redis host to ENV based configuration for Docker.

Signed-off-by: Marco Neumann <marco@crepererum.net>