[tex-live] pretest -> update texlive 2017

[Bob Tennent]

 >|> Is TL2017 not yet available at CTAN mirrors? Here's what I
 >|> get when I try to update from a pretest installation:
 >|>
 >|> /usr/local/bin/tlmgr:
 >|>  open tlpdb(ftp://ctan.math.ca/tex-archive//tlpkg/texlive.tlpdb) failed:
 >|>  at /usr/local/texlive/2017/tlpkg/TeXLive/TLPDB.pm line 360.
 >|>
 >|I already did updates from my mirror.

I've tried many mirrors and I get the same result. Also on
other systems.  

I presume I could re-install but I'd rather not have to do
that if the problem could be fixed more easily.

Bob T.