Fix open file hard limit, apache2 autostart, MySQL connection problems, ActivePerl, vert.x downloads

On Ubuntu Server, the hard limit is 4096, which is less than the
soft limit of 8192 that we're trying to use. Thus, to really use
a soft limit of 8192, we need to also boost the hard limit to
8192.

Disable apache2 autostart at boot.

If we want to use MySQL back_log=5000 (already set in my.cnf), we also need to set the OS-level net.core.somaxconn=5000. This solves database connection failures that I was seeing.

Retry ActivePerl downloads to deal with intermittent 404 errors.

Update vert.x download URL.