MAR-192: Fix environment indicator test:

- Expected content in the test was incorrect (probably old value from
messing around with improving the environment indicator).

MAR-197: Implement environment indicator for the web_server role:

- Now the environment indicator will also cover the default landing
page for the web server.
- Tweaked the landing page to look a bit better in terms of
margins (particularly important for the environment indicator).

MAR-189: Refactored web_server tests to be less hostname-dependent:

- Use the inventory name (alongisde distribution version) in places
where it's possible and makes sense to do so.
- Rearrange the IP allocation a bit to make more sense.
- Drop architecture information from the hostnames.
- Make the connectivity test operate over a matrix of input
parameters.
- Replace singular use of wget for testing with curl.

MAR-170: Always enforce use of HTTPS in the web_server role:

- Dropped the default_enforce_https parameter.
- Updated tests.
- Updated release notes.

MAR-158: Extended TLS cipher tests for web_server role for optional parameters:

- Extend the existing tests to cover both enabled and disabled
ciphers.
- Deduplicate list of all available ciphers for both testing of
mandatory and optional parameters.

MAR-158: Deduplicate tests in web server role:

- Deduplicate test for certificate validity check configuration
deployment.
- Deduplicate test for checking if TLS is enabled or not.

MAR-158: Split-up the TLS tests for web_server role:

- Better separation for testing individual properties of TLS
configuration (whether it's enabled, what protocols are enabled, and
finally enabled ciphers).

MAR-162: Make the default_https_tls_certificate and default_https_tls_key parameters mandatory:

- Dropped the defaults from web_server role.
- Updated group variables in role tests.
- Changed the key/certificate file extensions to be more descriptive.
- Updated role reference documentation.
- Updated usage instructions to include the mandatory parameters.

MAR-149: Switch to using File.content_string instead of File.content in tests for all roles:

- The .content variant returns contents as bytes, while the
content_string returns a string (which is what is wanted in
practically all cases).

MAR-129: Updated web_server role for Ansible 2.5.x and new Molecule:

- Fixed linting errors.
- Include global linting configuration file in the test configuration.
- Moved variables from the test playbook into group variables.
- Updated how hosts are referenced in tests.
- Fixed deprecation warnings.

MAR-128: Upgraded tests for ROLE_NAME role:

- Switch to new Molecule configuration.
- Updated set-up playbook to use become: yes.
- Moved some preparatory steps outside of the main playbook (eases
idempotence tests).
- Updated tests to reference the yml inventory file.
- Updated tests to use new fixture (host instead of individual ones).
- Switched to extracting hostname instead of hard-coding it in a
couple of tests.
- Renamed hosts instances to include Debian version in their
hostnames.
- Fixed some linting issues.