Use a smaller number for checking console log length
Use a smaller number for checking console log length

Not all images can return console log longer than 10 lines, e.g.,
Red Hat Enterprise Linux Server 7.0 will return console log
with 5 lines.
We don't know how many console log lines should an image return,
but generally speaking it's safer to use a smaller number so that
Tempest can be used for images other than cirros.

Change-Id: I7f6ffe5bdc6b7992fe15935d4f8498e8acf59453
Closes-Bug: #1783509

masayukig/tempest,openstack/tempest,cisco-openstack/tempest,cisco-openstack/tempest,openstack/tempest,masayukig/tempest