Avoid redefining host to none in get_instance_nw_info(...)

The host parameter is required and a part of the method signature.
When it is redefined from kwargs.get('host') the supplied value
gets redefined to None. This removes the redefinition and keeps the
parameter value intact.

Fixes bug #1194178

Change-Id: I779cbce909935a4b794c16cefb0128f16f8563fb
Merge "Avoid redefining host to none in get_instance_nw_info(...)"