If you are working with dates it is best to use datetime, and I don't like that date format, so I will answer using datetime. It should be possible to also use datestr if you really want to.
Looking at the busdays docs the holiday list used by default is for the US, but can be replaced with our own list of holiday dates.
As you want 0 holidays, you can make the list of holidays provided to busdays (and other functions like isbusday) that only contains data outside the range of your data. The holidays list you manually provide replaces the US-holidays data.
startDate = datetime(2017,12,11);
endDate = datetime(2017,12,15);
fakeHoliday = datetime(1,1,1); %Creates a datetime entry for 01-Jan-0001
date_vector = busdays(startDate,endDate,1,fakeHoliday)
%If it must be strings
formatOut = 'mm/dd/yy';
date_strs = string(datestr(date_vector,formatOut));
Though your provided date range doesn't include any holidays, so you need the actual range to see if it works.
