bug 1069359; init virtualenv on login

Pretty straightforward.  I expect that this will be (eventually) replaced by something more programmatic down the line, but imho, this is a convenient addition with little incurred technical debt. :money_with_wings:

@rhelmer @bramwelt `r?`
`-r` does indeed test if the target exists and is readable; however, it does not verify that it is a *file*, hence the `-f`. Consider:

```bash
#!/usr/bin/env bash

DIR='a_dir'
FILE='a_file'

mkdir $DIR
touch $FILE

for i in $DIR $FILE; do
  if [ -f $i ]; then
    echo "-f ${i} TRUE"
  fi

  if [ -r $i ]; then
    echo "-r $i TRUE"
  fi
done

rm $FILE
rmdir $DIR
```
Output:
```
[vagrant@localhost ~]$ ./tester.sh
-r a_dir TRUE
-f a_file TRUE
-r a_file TRUE
```