tests: make directory to prevent test process from going out of $TESTTMP
Before this patch, test process for test-bookmarks.t goes out of
$TESTTMP at "cd .." before creation of "orderrepo" repository.
To prevent test process from going out of $TESTTMP, this patch makes
directory "repo" sub-directory and executes almost all test scenarios
in test-bookmarks.t under it.
This is preparation for new test added in subsequent patch.
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).