ci.jpl: Only parse output.log when LAVA tests available

Jenkins should not try to parse output.log when there is no tests
submitted to LAVA. Because output.log will not be generated and finally
unexpected NoSuchFileException will be caused.

Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
Change-Id: I2faf0da5221cc377aeb8b1490df691e4d10b82fb
1 file changed