crosperf: use compact status output

Previous, it shows the status as
FAILD: benchmark(1), benchmark(2), benchmark(3)
After the change, it shows
FAILD: benchmark(1,2,3)

BUG=chromium:564890
TEST=it shows the status in the right way.

Change-Id: I714a66d75dcabb7a3146acd67190a85064b82b32
Reviewed-on: https://chrome-internal-review.googlesource.com/241045
Commit-Ready: Yunlian Jiang <yunlian@google.com>
Tested-by: Yunlian Jiang <yunlian@google.com>
Reviewed-by: Caroline Tice <cmtice@google.com>
1 file changed