Refactored router module

Expanded and fixed module results docs.

Moved ext_ips_spec into the module class because global scope is not
necessary. Renamed it to external_fixed_ips_spec to explain its
purpose.

Sorted argument_spec and attribute docs by attribute name and fixed
indentations. Marked router attributes which cannot be updated.

Mark network attribute as required by enable_snat and
external_fixed_ips attributes. Fixed docstring of network attribute:
Module attribute interfaces does not require the network attribute,
its external_fixed_ips what requires network to be set.

Changed examples from deprecated ip to current ip_address attribute.

Dropped self.fail() calls and let openstacksdk handle missing networks,
subnets.. instead because less code means less code to maintain.

Limited line length to 80 chars to be consistent with other OpenStack
projects. Personally, I prefer a 120 chars limit but consistency is more
important.

Added explanation in code comment why we cannot update a router's name.

Moved upfront cleanup operations in router's integration tests to the
beginning of the role.

Assigned meaningful names to result variables
in router's ci role to easily identify which modules produced the
data.

Added tests for router ids, admin state and interfaces.

Change-Id: Icae77a43479fb4f0bae065d1c5d7942cb0f5fd6b