WL-124 added the jasmine tests for the autoenrollment csv

@afzalwali @asadiqbal08 
@chrisndodge  Kindly review the changes for WL-124.
__file__ has the value '/edx/app/edxapp/edx-platform/common/test/acceptance/pages/lms/instructor_dashboard.py'

split() splits by the OS dependent '/' or '\' separator to gives us a list of folders reaching till the actual filename :
(Pdb) __file__.split(os.sep)
['', 'edx', 'app', 'edxapp', 'edx-platform', 'common', 'test', 'acceptance', 'pages', 'lms', 'instructor_dashboard.py']

the [:-5] gets rid of the last 5 items in the list, leaving us with a parent folder where we can append the the actual path of the file on the system:
(Pdb) __file__.split(os.sep)[:-5]
['', 'edx', 'app', 'edxapp', 'edx-platform', 'common']

We then join these again to make /edx/app/edxapp/edx-platform/common
In the end, we append the file path to reach the exact file. e.g. 
/edx/app/edxapp/edx-platform/common/test/data/uploads/auto_reg_enrollment_errors_warnings.csv

There would be many better ways to achieve this, I just used the first one that worked. One change I might make is to use [:-7] to exclude the 'common' and 'edx-platform' as well and add it to the string I am appending to make it '/edx-platform/common/test/data/uploads/%s' % file_name. This might make browsing to the actual file simpler for someone looking at the code.

Since the bokchoy tests work with the browser, and the browser is not aware of the code repository, we cannot give it a relative path. The browser requires the full path on the system to can pick an actual file.

I hope this is acceptable as-is.