cr-daily-branch, cr-publish-flight-logs: Tolerate failure to push harness

cr-daily-branch, cr-publish-flight-logs: Tolerate failure to push harness

Provide cr-publish-flight-logs --push-harness-try, which attempts the
push but doesn't mind if it fails.

If we are not --real, tolerate failure to publish the flight logs.

Also, honour OSSTEST_PUSH_HARNESS which might contain '' or
--push-harness or --push-harness-try.

CC: Roger Pau Monné <roger.pau@citrix.com>
Tested-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>