Move pids up to install root to prevent "folder *not* empty" problem

SO... the problem that we had with empty deploys directory has to do with how I was tracking running slug installations. I was storing a PID file in the folder so that I could then use those PID files to find the other running installs. The problem was that I created them in the INSTALL_DIRs. This meant that when we went to check if the folder was empty, it *absolutely* was not. :frowning:

This change moves those PID files up to the INSTALL_ROOT, which gets rid of that problem. I manually hacked this into a FPM 1.1.0 created slug and the install started working.

@Tapjoy/opsautomation