Convert GitHub wiki content to readthedocs.io (sphinx)

[pevik]

The rest of GitHub wiki content in doc/old should be converted to https://linux-test-project.readthedocs.io/ (sphinx).

Converting to headers:

• doc/old/C-Test-API.asciidoc
• doc/old/C-Test-Network-API.asciidoc
• doc/old/KVM-Test-API.asciidoc
• doc/old/namespaces-helper-tools.txt (Less priority, put to the source code of tools in testcases/lib/)

Separate page for shell (sphinx IMHO does not support shell):

• doc/old/Shell-Test-API.asciidoc