Allow selecting the network for doing the ssh with

Previously, nova ssh was searching for network types: public and
private, which seems to be incorrect (fixed and floating seems to be
correct), causing that this command has probably never worked.

This commit fixes the above and adds an option for selecting the network
to use, which is helpful when there are more networks for the VM.

Change-Id: I01ea6cee725c0feaacab60975c3792b0ac1305e9
Closes-Bug: #1227694
Closes-Bug: #1343991
Enable several checks and do not check docs/source/conf.py

* E265 block comment should start with '# '
* H302 import only modules

Do not check docs/source/conf.py. The file is imported from the
cookiecutter template.

Documented why checks are ignored and if they should be enabled
in the future.

Change-Id: I367064ecaa6d1fd9d918f7ce003303e2db660647
Merge "Allow selecting the network for doing the ssh with"
Merge "Enable several checks and do not check docs/source/conf.py"