admin scripts: script to run conn hooks for mongodb carts

This commit adds run-mongodb-connection-hooks.rb, intended to be run on
the broker, which automates running the connection hooks for any app
using the mongodb-2.4 add-on cartridge. This is specifically to update
the `PATH` and `LD_LIBRARY_PATH` variables for scaled carts after
updating to a new version of the `openshift-origin-cartridge-mongodb`
package.

Enterprise bug 1135062
https://bugzilla.redhat.com/show_bug.cgi?id=1135062
install: enable xpaas install experience

https://trello.com/c/5e9f2ejA/275-5-xpaas-preparedness

Changes to openshift.sh so that when the fuse cartridge is released, we
have an "xpaas" profile that can work with it out of the box.

This also makes some generalized changes:
* Introduce a setting for proxy ports per gear
* Introduce a setting for district UID range
* The SNI proxy is installed, configured, and firewall ports opened
* Introduce settings for SNI proxy port range

Then, when a node is designated with node_profile=xpaas:
* External ports per gear defaults to 15
* The SNI proxy defaults to listening at 10 ports
* xpaas districts are created with reduced capacity (to match 15 ports)
install: organize header comments

The comments, particularly the parameter listing, had grown somewhat out
of control. They are now organized into hopefully-logical sections with
a table of contents.

No code changes were made.