create make command to run litmus tests

[individual-it]

to make it even easier to run the litmus tests, hide the complexity behind a make command
https://github.com/cs3org/reva#litmus-tests

[jimil749]

Hi @individual-it @ishank011! I thought of giving this a shot. But when I tried to run the tests locally as per the README provided, I run to error reading the configuration file(s): open storage-oc.toml: no such file or directory.

This is because storage-oc.toml does not exist. I think in the README, we need to change storage-oc.toml to storage-users.toml. Should I open a PR to rectify the change?

And then maybe, I'll try to implement the make command. :)

[phil-davis]

Should I open a PR to rectify the change?

Yes please. The "ownCloud legacy integration tests" section of README was updated in PR #1452 but the "litmus tests" section was missed!