Rose stem installs to ~/cylc-run/rose-stem

[wxtim]

Describe the bug

When $PWD is not a subversion repo rose stem --source=X=$PWD is unable to get a name for the workflow install directory and installs the workflow in ~/cylc-run/rose-stem. Ideally the basename of the source directory should be used.

Expected behavior

rose stem --source=X=/home/h02/tpilling/cylc-src/example
...
- INSTALLED example/run1 from /net/home/h02/tpilling/cylc-src/example/rose-stem
+ INSTALLED rose-stem/run3 from /net/home/h02/tpilling/cylc-src/example/rose-stem

Pull requests welcome!
This is an Open Source project - please consider contributing a bug fix
yourself (please read CONTRIBUTING.md before starting any work though).

[wxtim]

At Cylc 8 this is a potentially problematic bug for some users, because they won't be able to reinstall with

WorkflowFilesError: Failed to install from /path/tims-rose-stem/rose-stem: previous installations were from /path/bb/rose-stem