Add more scripts to alternatives system

Currently, stackforge cookbooks execute a number of different -manage
scripts.  This change adds more of these scripts to the alternatives
system so the cookbooks can find these scripts under /opt/openstack
correctly.
Add nova-dhcpbridge to alternatives

In my testing I'm using nova-network and this appears to require
nova-dhcpbridge to exist in /usr/bin (unless dhcpbridge specific in
nova.conf file).
Merge pull request #4 from mattt416/update_commands

Add more scripts to alternatives system