scripts/test: Add option to run all test cases in a single OSv instance

Previously, scripts/test.py had no option to do that. It launched an OSv
instance for each test case.
Terribly slow PCs like mine took a bunch of time to run all test cases
through 'make check'.

Then let's take advantage of testrunner.so which will use a single OSv instance
to run all test cases, consequently boosting the speed considerably.
Let's also change testunner.so to conform our needs, e.g. blacklist.

To run this fast check, do: scripts/test.py --single;

Results show that this option is about 2.5x faster than the current one.

By now, let's not use this approach as the default version given that its
output has to be better formatted.

Signed-off-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
Fix tests/testrunner.cc coding style

Start using spaces instead of tabs and surround all single-line
control statements with curly braces.

Signed-off-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>