If the main CI job fails before generating an ARA report, the SQLite
database file will not exist. This cases the job to fail with
POST_FAILURE, rather than FAILURE, and the following is seen in the
logs:

rsync: change_dir "/home/zuul/.ara" failed: No such file or directory
rsync error: some files/attrs were not transferred (see previous errors)
(code 23) at main.c(1655) [Receiver=3.1.1]
rsync: [Receiver] write error: Broken pipe (32)

This change fixes this by checking for an SQLite database file, and only
intiating the rsync transfer if it exists.

Change-Id: I370e5bc9f137abe552918a3215a025fa61e3a0ca