`GUROBI_HOME` check does not work with pip installation of Gurobi

Describe the bug If Gurobi is installed via pip (see e.g. here), then the .so file does not conform to the current style set out in mip/gurobi.py.

To Reproduce

1. pip install mip
2. pip install -i https://pypi.gurobi.com gurobipy
3. `setenv GUROBI_HOME=‘xxx’
4. It doesn’t work

Expected behavior I think it would be nice if it happened.

Desktop (please complete the following information):

• Operating System, version: Linux [note: this does not happen under Mac]
• Python version: 3.7
• Python-MIP version (we recommend you to test with the latest version): latest

Additional context I think a possible fix would look like this, i.e. to add this after the first is not libfile:

if not libfile: # For pip installer
            libfile = glob(
                os.path.join(os.environ["GUROBI_HOME"], "gurobipy.*.so")
            )

For Linux, the .so file is named: gurobipy.cpython-37m-x86_64-linux-gnu.so. This would though mean that the version number deduction with major_ver and minor_ver in gurobi.py does not work and the subsequent definition of lib_path does not work either. Not sure how to handle this, which is why I did not make a PR.

[RichardOberdieck]

Yes, this is unfortunately to be expected since the trial license only works for gurobipy or our command-line interface (gurobi_cl); it will not work with any other API, including the C API.

I will ask internally whether we can change this, and will let you know if I hear anything back.

[DavidWalz]

A workaround for windows is to copy the gurobiXX.dll file inside a folder called /bin because of this line https://github.com/coin-or/python-mip/blob/14466736d92ea13182d18c61c64642aff4a5a2e8/mip/gurobi.py#L55