* Tidy mount module for testing
Fix spelling mistakes in comments. I *think* the example for omitting parents
root has the wrong parent ID.
Make mountinfo file a parameter for testing.
* Don't strip leading slash from mounts
The current code does not follow the example, it produces src=tmp/aaa instead
of src=/tmp/aaa. This causes problems with bind mounts under /rootfs.
* Use dictionary to store mounts by ID
Instead of looping over each one to check if the ID matches. This does not
preserve the order of the output on < Python3.6, but that is not necessary.
* Make linux_mounts a dict
Always accessed by 'dst', so avoid looping by just making it a key.
* Add test case for get_linux_mounts
