change location of valgrind output files to something less obnoxious

<div id="comment:0"></div>

When running 

``` 
  sage -valgrind
```

the output files are all over in $HOME/.sage.  They should be put in a file 

```
  $HOME/.sage/valgrind
```


Component: **packages: standard**

_Issue created by migration from https://trac.sagemath.org/ticket/1147_

