Add the ability to adjust when haproxy shutsdown the app cart in the lead gear

https://bugzilla.redhat.com/show_bug.cgi?id=1013166

Currently, haproxy, when scaled to 3 or more gears, will shutdown the 
application cartridge (i.e. ruby, python, php, etc) in the gear that also
houses haproxy so that haproxy has access to the entire gear's resources. It
is requested that the number of gears required to shutdown the application
cartridge be adjustable.

The goal of this is to allow the application creator to have one haproxy gear
and just one application gear or , if load permits, have 3 total gears and
still have the application cartridge running on the haproxy gear.