autotest: wifi: When applying SSID suffix, limit length

Some default SSIDs can become too large when a suffix is added.
Limit the SSID string length under these conditions.

BUG=chromium-os:31339
TEST=Re-run autotest

Change-Id: Ib8fded679ce631c7a961f28b7dee0805fdd52683
Reviewed-on: https://gerrit.chromium.org/gerrit/23925
Reviewed-by: Stanley Wong <stanleyw@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
Commit-Ready: Paul Stewart <pstew@chromium.org>
1 file changed