CLN GH10559 Rename sheetname variable to sheet_name for consistency
- [x] closes #10559
- [x] tests added / passed
- [ ] passes `git diff upstream/master | flake8 --diff`
- [ ] whatsnew entry

reason you closed this?
 Hi jreback, I did not mean to close the pull request. This is my first attempt at contributing and I'm going through some growing pains. I realized as soon as I submitted the request that I had accidentally changed the keyword arguments instead of keeping them as sheetname. I will make another attempt at fixing the issue if that's okay. 
 contributing docs are [here](http://pandas.pydata.org/pandas-docs/stable/contributing.html)
 pls reopen if you like to rebase / update
 Hi @jreback, sorry for going M.I.A. on this. I want to fix this issue, but I have a few questions. When you say sheetname=None, do you mean you want to change sheetname=0 to sheetname=None? If this is the case, my plan is to change these arguments in read_excel() and _parse_excel() while also adding a deprecation warning. Please let me know your thoughts.
 so you rename the arg as you did, then add the deprecated kwarg at the end, e.g. `sheetname=None`, so then you can pick it up both if its passed positionally (e.g. `sheet_name` will be set), then you can issue a warning if the `sheetname` kwarg is set you can issue a warning 
 @jreback Hi cloned the fork and created a dev environment by using python setup.py develop. When I made the necessary changes, I noticed that all of the tests still passed when they shouldn't have. I read the docs again to see if I missed anything, and asked on IRC, but we couldn't come up with a solution. Is there something I need to be doing with nosetests in order to run a similar test suite to the one on Travis?

Thanks,
Mandeep
