FTS REST Clients should look for the "fts3client.cfg" file in the user home directory

Currently the FTS-REST Clients look for the config file in /etc/fts3/fts3client.cfg. This is not a good location for a client config as users don't have write permissions in /etc directory. This shows up especially in systems such as lxplus.

Additionally, since the fts-rest-client RPM package installs this config file, it also needs to install the /etc/fts3 directory, which conflicts with the fts-server RPM, leading to the following error:

Transaction check error:
  file /etc/fts3 from install of fts-rest-client-3.12.0-1.el7.noarch conflicts with file from package fts-server-3.12.1-1.el7.cern.x86_64

Proposal
The FTS-REST Clients should not install the fts3client.cfg anymore. More so, they should look for such a file under the ~/.fts3client.cfg location.