Move the get interface logic outside of ifconfig into libtools.lib

Expose the logic of getting the interface outside of ifconfig
implementation and allows other module to use it.

The implementation hide the bsd related details from modules that uses
it.

Signed-off-by: Avi Kivity <avi@cloudius-systems.com>
Http Server: Add an API to unset environment variable

This adds an API and a test to unset an environment variable.

Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>