rust: Add require_root and vendor install base

Adds the require_root property to rust_test modules so that tests can
run as root. Also adds an install base to allow vendor tests to install
to a different path, otherwise installs to 'unrestricted' like cc_test.

Bug: 200602232
Test: test with require_root: true runs as root
Test: test installed to new base directory
Change-Id: Ifa716871ff87471f0c0caff7af558d47db85ccd1