ENH: Add support for s3 in read_excel #11447
closes #11447 

Updated excel.py to use pandas.io.common.get_filepath_or_buffer (handles s3 urls) instead of urlopen, only when _is_s3_url returns true.    This was the minimally invasive change.

tests pls
 pls add a test for this. you can post an `.xls` file and I will put it up on the pandas s3 bucket.
 pls add a whatsnew note as well (enhancements)
 Will do. What's the path to the s3 bucket?
Will use [test1.xls](https://raw.githubusercontent.com/pydata/pandas/master/pandas/io/tests/data/test1.xls) and [test1.xlsx](https://raw.githubusercontent.com/pydata/pandas/master/pandas/io/tests/data/test1.xlsx) for testing if you can put them in the bucket for me.
 ok I uploaded those 2 files to the standard bucket `https://s3.amazonaws.com/pandas-test/test1.xls` and `.xlsx`. lmk if you cannot access them.
 Can you go ahead and add [test1.xlsm](https://raw.githubusercontent.com/pydata/pandas/master/pandas/io/tests/data/test1.xlsm) to the s3 bucket as well?  Looks like the existing excel tests use all three extensions and I want to use the same base class.   
 ok, should be good to go.
 ok, PR updated with test case and whatsnew note.
 perfect. needs a rebase (prob a doc conflict), then ping when green.
 also can you extend the doc-string for `read_excel` (similar to how `read_csv` is done) for the s3
 Looks like the doc for `read_excel` already mentions s3 in the same way as `read_csv`.  Does this work?
...`Valid URL schemes include http, ftp, s3, and file.`...
 Hmm, also looks like I [broke the build.](https://travis-ci.org/pydata/pandas/jobs/94190434) The unit test is failing when trying to import boto to handle the s3 url: `ImportError: No module named 'boto'` 

Is there a config I need to update for the CI process to install boto?
 Ahh, I see I can just implement a `nose.SkipTest`.  Will add a `_skip_if_no_boto()`
 yep - builds have different deps / versions of things to give code a workout
 Good stuff! Ok, I think everything is good to go now.  Thanks for walking me through my first contribution.
 @parsleyt thanks for the contribution!
