incorrect references to $GLOBUS_LOCATION/etc/globus-user-env.sh

Hello, following the instructions here: http://toolkit.globus.org/toolkit/data/gridftp/quickstart.html, as well as in the script /etc/grid-security/sshftp (symlink to /etc/gridftp-sshtfp), they try to source $GLOBUS_LOCATION/etc/globus-user-env.sh, however this doesn't exist in this location when using `apt` method (on Ubuntu 16.04).

The correct location of the file is:
```
user@host:~$ dpkg-query -S globus-user-env.sh
globus-common-progs:amd64: /usr/share/globus/globus-user-env.sh
```
($GLOBUS_LOCATION=/usr, according to that script and others. There is no /usr/etc/)

I'm not sure if this is a bug in the documentation, or if the debian/ubuntu repositories should update the 'gridftp-sshftp' script. The `globus-url-copy` command functions (for localhost example) without sourcing the globus-user-env.sh, but maybe it would fail for something more complex.