Adapted environs storage tests for Windows.

Made some minor adaptations to the storage-related tests in environs to work on Windows as well.
The only test still failing is TestPathRelativeToHome, which will work just fine once [this pull](https://github.com/juju/utils/pull/27) gets merge into the utils package and tilde expansion works on Windows as well.
Well the whole change consists of the fact that on Windows there would be discrepancies due to the program (correctly) producing outputs with backslashes whilst the baselines feature slashes.
As of recently, the SamePath checker introduced into the testing package can be used in such situations, however, it only handles one path at atl time, hence the need to iterate over the lists.
Point is, considering that the initial test was done with Assert as well, and there is nothing after that particular line that would need running, I feel that Assert is the way to go here as well. Anyway, the failure notices would look the same, with the difference that if we used Cgeck you'd get a lot more of them(one for each failed check).
I can change it to Check if you insist, I just wanted to stick to the original as much as possible whilst making the test valid on Windows...