runqemu-internal: provide more info if a preconfigured tap is used

runqemu-internal: provide more info if a preconfigured tap is used

We should provide the user more information if a preconfigured tap
is used. This is because the user might have manually set up the tap
interface to be used by other qemu binaries.

So at a minimum, we should let the user know how to make runqemu skip
that tap interface.

[YOCTO #5047]

(From OE-Core rev: ec08d92641cc51c567cc3745937b1839d3faa095)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>