scheduler daemon: add unit test for looping mode
scheduler daemon: add unit test for looping mode

This was done while investigating bug #1282515, but I couldn't find the
problem yet. At least we have an extra unit test now.

https://bugs.launchpad.net/lava-server/+bug/1282515

Change-Id: Ib365ee05b05e29c04b5fd3f52fd4258209757546

OSSystems/lava-server,Linaro/lava-server,OSSystems/lava-server,Linaro/lava-server,Linaro/lava-server,Linaro/lava-server,OSSystems/lava-server