Construct ssh_dir variable using concatenation syntax

I'm not sure why, but I don't think the ``{{ pillar[] }}`` syntax works within _vars.sls. I fixed it with +. Otherwise it created a directory structure like this and put .ssh/ into a folder named ``{{ pillar['project_name'] }}``:
```
/home# ls -la
total 24
drwxr-xr-x  6 root     root     4096 Jan 25 20:09 .
drwxr-xr-x 24 root     root     4096 Jan 25 20:11 ..
drwxr-xr-x  4 copelco  copelco  4096 Jan 25 20:17 copelco
drwxr-xr-x  3 myproj myproj 4096 Jan 25 20:07 myproj
drwx------  3 myproj myproj 4096 Jan 25 20:09 {{ pillar['project_name'] }}
drwxr-xr-x  4 ubuntu   ubuntu   4096 Jan 25 20:01 ubuntu
```