run.py: Add -V (--verbose) option

The OSv loader has a "--verbose" option to enable debug() output to be
printed to the console and not just to a memory buffer. However, needing to
pass this option in the "-e" string is annoying, and even worse when you want
to use the default command line and didn't even want an explict "-e" option.

So this patch adds a --verbose to run.py, which can be used whether or not
a "-e" option is given. For example:

    run.py --verbose
or
    run.py --verbose tests/tst-timerfd.so

As a shorthand for --verbose, I used "-V". Unfortunately, lowercase "-v"
was already taken (by the "vhost" option).

Fixes #173.

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>