'berks list' does an implicit 'install'

New to Berkshelf and playing the game of "where's my cookbook" I discovered that running 'berks list' inside a cookbook directory runs an implicit 'berks install'  Is that the  expected behavior?    I would expect the 'list' call to return empty until 'berks install' is explicitly run on the cookbook.

```
mymac:cookbooks$ berks shelf list
There are no cookbooks in the Berkshelf shelf


# go into wrapper cookbook directory and see what's in the berkshelf
mymac:cookbooks$ cd wrapper_cookbook
mymac:wrapper_cookbook$ berks list
Cookbooks installed by your Berksfile:
  * wrapper_cookbook (0.1.0)
  * logrotate (1.3.0)

# look at what is 'installed' on my berkshelf 
mymac:wrapper_cookbook$ ls ~/.berkshelf/cookbooks/
logrotate-1.3.0


#check the shelf
mymac:wrapper_cookbook$ berks shelf list
Cookbooks in the Berkshelf shelf:
  * logrotate (1.3.0)


#leave wrapper_cookbook and look at shelf.
mymac:wrapper_cookbook$ cd ..
mymac:cookbooks$ berks shelf list
Cookbooks in the Berkshelf shelf:
  * logrotate (1.3.0)

```