[vpython] Include UID in venv name.
[vpython] Include UID in venv name.

This will prevent e.g. `chrome-bot` and `root` from trying to share the
same virtualenv in e.g. the same swarming named cache.

R=tandrii@chromium.org, 9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org

Bug: 869227
Change-Id: I415bc0af9478e0253744582a64c45be60a59c6de
Reviewed-on: https://chromium-review.googlesource.com/c/1340622
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Commit-Queue: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Auto-Submit: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

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