Implement fix-permissions verb.

- Recursively change ownership of ROS HOME to current user.
 - Fixes: https://github.com/ros-infrastructure/rosdep/issues/332
Getting this stuff right is such a pain in 2.7. I think the cleanest solution to have all strings always unicode everywhere, but we won't change that in rosdep.

In python 2.7:

```
In [46]: "foo %s" % u"bär"
Out[46]: u'foo b\xe4r'
```

```
In [44]: "foo {0}".format(u"bär")
---------------------------------------------------------------------------
UnicodeEncodeError                        Traceback (most recent call last)
<ipython-input-44-3eb72b173b3d> in <module>()
----> 1 "foo {0}".format(u"bär")

UnicodeEncodeError: 'ascii' codec can't encode character u'\xe4' in position 1: ordinal not in range(128)
```