Add llvm_next_builder to list of known builders.

This will fix the problem with rotating builders; they were
updated to use the llvm_next builder, but this script was not updated
to use llvm_next.

BUG=chromium:674804
TEST=Tested in role account on chrotomation2, launching rotating
builder.

Change-Id: Ifd4ba57cf403feae0b0b84c8b21accb34987ecbc
Reviewed-on: https://chromium-review.googlesource.com/424893
Reviewed-by: Yunlian Jiang <yunlian@chromium.org>
Commit-Queue: Caroline Tice <cmtice@chromium.org>
Tested-by: Caroline Tice <cmtice@chromium.org>
1 file changed