dabbad: add pidfile input parameter.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
test: use pid file to stop dabbad instance.

Kill all dabbad running instances after a test is overkill.
It is also a nice step towards parallel testing.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
Merge pull request #12 from eroullit/pidfile

Add dabbad cli option to create pidfile at specific path