Update makefile to hunt for pip/nose bins.

- Check for nose/pip in both venv/bin and venv/local/bin
- Remove the venv and develop dep for the test target since pip won't exist
until post-install and tries to use the wrong path and files.
- This means tests need to be run after a manually make install which is the
default target.

git clone
cd amulet
make
make test
Merge pull request #10 from mitechie/find-venv-bins

Update makefile to hunt for pip/nose bins.