Make respawn behavior of EventLogging consumers more resilient

If the database goes into read-only mode (as happened today), the MySQL
consumer on vanadium fails to insert records. The time from service start to
crash is very quick, so it hits Upstart's default respawn thresholds and
Upstart gives up before the database has had a chance to recover. This patch
specifies a 5-second sleep interval between restarts and sets the respawn
threshold to >30 attempts in a five-minute period.

Change-Id: Idaefb8958cd996a5581d708e4a596f56dbdcb599