Write unit test for LVM device manager's creteNS() functionality

[avalluri]

As pointed in #688 (comment), currently, there are no tests for validating if the LVM device manager uses only requested pmemPercentage out of available PMEM space of a region. This is a bit complicated as the testing this requires underlined PMEM region/namespace properties.

It would be good if we could find a way to develop a test case for this. As suggest by @pohly, one way is making createNS() work on an interface, so that tests could have a mock implementation.

[pohly]

We already had two bugs in that code (fixed by #714):

• did not ignore regions in the wrong mode (not sure how relevant)
• caused restart of driver (did happen each time the driver ran for the first time on a node)

[okartau]

I just detected a third bug, fix in #717
I agree, unit test code would help significantly. One of the bugs was regression caused by omitted code lines in function move where original code was correct.
We cant have really same what comes form HW, but we can use some pre-defined sets of typical value combinations.

[pohly]

We do have infrastructure for mocking libndctl now in https://github.com/intel/pmem-csi/tree/devel/pkg/ndctl/fake

That could be used for this.