When looking for task ID in output of koji runroot command, do not check
just the first line. Instead look for first line that contains just a
number.
Most of the time, this should really be the first line. But if koji
client decides to print any warnings, this patch should skip that.
JIRA: RHELCMP-8944
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>