Restores the working directory

[giswqs]

Running WBT tools will change the current working directory due to os.chdir(self.exe_path). This is causing issues for other packages affected by the working directory. This PR restores the working directory after running a WBT tool.

try:
    work_dir = os.getcwd()
    os.chdir(self.exe_path)
except (OSError, ValueError, CalledProcessError) as err:
    callback(str(err))
    return 1
finally:
    os.chdir(work_dir)