run-tests: enforce the drive letter from `getcwd` to upper case
For some reason os.getcwd() can return either `c:` or `C:` depending of which
binary you used on Windows. We normalize this to `C:` and the like. This fix
`test-run-tests.t` on windows as the drive letter in "$TESTTMP" was "wrongly"
set to 'c:/' if the test path wasn't explicitly specified.
Differential Revision: https://phab.mercurial-scm.org/D11035
Run Mercurial tests with Vagrant:
$ vagrant up
$ vagrant ssh -c ./run-tests.sh