[bbagent] Use non-root directory for the Dev mac builder
[bbagent] Use non-root directory for the Dev mac builder

bbagent binary gets removed under $CWD which might be the root cause of
dev Mac builder failure. Changing to use another dir to see if it solved
that issue. This CL will be reverted together with https://crrev.com/c/3546788

Bug: 1297809
Change-Id: I1ce1a547826734b24e0ed638789a17f7ef848a9e
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3550159
Reviewed-by: Chan Li <332b6c56634d0f63001046c664a2370006a02420@chromium.org>
Commit-Queue: Yuanjun Huang <a5f4b8445ce5e958d19c0a7caeadcd07c9d18770@google.com>
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go