Add automatic resource cleanup to FileSystem and File tests

[lookeypl]

Some tests related to FileSystem and File (ex. FileSystemTest::TouchFile) create a file during the test. In case of failure, the file will stay and future test calls will fail earlier because the test file already exists. Investigate all possible places where such thing might happen and implement a solution to fix it. Probably a FileRAII might be a good idea here - see what will be the best for these tests.

[Witek902]

Maybe just put all test files in some "TestData" folder and modify python script so it's always removed after running the tests?

[lookeypl]

This should be done by tests themself, not by the test script. Someone can call "Bin/x64/Release/nfCommonTest.exe" directly (I do that sometimes) and then nothing will remove the files.

[mkulagowski]

Can't You put them into folder and overload gtest's TearDown() to delete the folder recursively, if it exists?

[lookeypl]

@mkulagowski it is one of the solutions. Assignee will have to do the investigation and choose what is best for our tests. ;)