I think I finally fixed it. My solution in case it helps others...
1. I upgraded to Ubuntu 16.04 (this may or may not be necessary as I have a feeling it was other fixes that solved it).
2. Set a password for the bitcore user. I.e. after doing the
do the following
nvm use 5.0
sudo useradd -r -m bitcore
sudo usermod -aG sudo,adm bitcore
sudo passwd bitcore
Now bitcore has access to some files it needs to modify when installing.
Finally the bitcore docs were missing the line
and once that was added it all installed as expected.
Using node 5.0.0
Using nvm 0.31.1
Whilst I've not tried running bitcore yet, the installation had no errors and thought I'd share this post before I forget what I did.
OMG I have been looking for this answer all over the internet. THANK YOU, this finally make it work.
The solution is not even in the bitcore forum.
Sorry to unearth this post but I think it is worth it.