Fix LOG_PATH to use 7char uuid

The zuul variable, LOG_PATH, is meant to be in the format of how
openstack stores its logs. OpenStack actually only uses the first 7
characters of the uuid in the path so we need to limit what we send
via the gearman variables here too

Change-Id: I2a3260c242e1fe895c650df276951ef23d7dc7c9
Merge "Fix LOG_PATH to use 7char uuid"