Added C9800cl support to cat9kv node type.

[torbbang]

Adds C9800-CL wireless controller support to the existing cat9kv node type.

Changes:

• Auto-detect platform from filename ("c9800" → cisco_c9800cl)
• Auto-detect hostname from image file
• Update README with usage examples

Both Cat9kv and C9800-CL qcow2s can coexist in the same directory.

Note:
I appreciate that this is something that likely won't see much use by other people than me - and I will just continue building the c9800-CL as a regular Cat9kv node if this change is deemed to be superfluous.