The setup step for Jenkins jobs was always running `pip install --user rbtools` before applying a patch. If the workspace within Jenkins already had a virtualenv this would fail entirely, and even if not, it was wasteful to do it every time. This now checks whether rbt is already on the PATH and only installs it when needed. When it is missing, rbtools is installed into a virtualenv in the workspace (reused across builds if present) rather than into the user site directory. The rbt patch invocation has also been reworked to pass the command as an array instead of building a string and then splitting it on whitespace. Testing Done: Created a Jenkins testbed and verified that the first time a Review Board job was triggered, it created a virtualenv and installed RBTools, and thereafeter it reused it.