We create a new log entry when a new series revision appears.

The series_revision_complete event only fires when the series/revision
is fully complete, eg., the git send-email series has been fully
processed. That behaviour is tested, making sure an incomplete series
doesn't appear in the SeriesLog table.

v2: Rebase on top of SERIES_DEFAULT_NAME changes

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>