Add Firedrake downstream CI (#426)

* Add draft Firedrake downstream CI

* Add human-readable name for Firedrake CI

* Fix firedrake source path in Firedrake downstream CI

* Fix permissions on Github homedir in Firedrake downstream CI

* Tweak pytest flags for Firedrake downstream CI

* Add tmate debug for Firedrake CI

* Tweak some permissions for tmate debug

* tmate hack

* chmod

* perm hack

* Show exception messages by default in Firedrake

* Pull in pyop2 patch for Firedrake downstream CI

* Fix pyop2 cd in Firedrake CI

* Install pyop2, fix loopy install for firedrake CI

* Do not pip install pyop2 for Fdrake after all

* Use -f in pip uninstall loopy for Firedrake

* Use -y in pip uninstall loopy

* Fix permissions for loopy install in Fdrake CI

* Firedrake CI: Check out loopy submodules, too

* Fix workflow syntax for loopy checkout in Fdrake CI

* Get loopy submodules manually in Firedrake CI

* Go back to actions/checkout@v1 for Firedrake CI

* Fix git submodules spelling in Firedrake CI

* Run firedrake pytest without --capture=no