Revert of Decrease swarming shards for Linux RandomOrder bots from 18 to 6. (patchset #1 id:1 of https://codereview.chromium.org/2835903002/ )

Reason for revert:
Want to go back to 18 shards to increase likelihood of single shard failure issues.

Original issue's description:
> Decrease swarming shards for Linux RandomOrder bots from 18 to 6.
>
> Review-Url: https://codereview.chromium.org/2835903002
> Cr-Commit-Position: refs/heads/master@{#466599}
> Committed: https://chromium.googlesource.com/chromium/src/+/e510777b49ba34c52aebc3613552cf2f4acbc2dc

TBR=mcgreevy@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.

Review-Url: https://codereview.chromium.org/2842973002
Cr-Commit-Position: refs/heads/master@{#467279}
1 file changed