The prepare_service() function is defined both in watcher/service.py
and in watcher/common/service.py.
These 2 needed to be merged into a single one
to avoid code duplication.
At the same time, the watcher/service.py only contains this function,
so I removed that file.
Change-Id: I0c935dfcd011bee9597315752dae8668221c53f9
Closes-Bug: #1525842