Change default rabbitmq port 5672 => 8672

Although 5672 is the IANA registered port for rabbitmq, on Redhat-6
based systems the qpidd service runs on that port. To avoid conflicts
with this service as well as to avoid conflicts with system installed
rabbitmq, the default port for chef-server's rabbitmq is now
8672. This value was chosen by incrementing the first digit of the
default rabbitmq port until a non-IANA assigned port was found.

The two chef-server services that connect to rabbitmq are
chef-expander and erchef. Both render the rabbitmq port in their
respective config files which have restart notifications for the
service.

rabbitmqctl communicates with the rabbitmq server using Erlang
distribution and does not rely on the listen port of the rabbitmq
server.

[CHEF-4346]
Rename OmnibusHelper function chef_status => service_up?

This better reflects the behavior which is to return true if the
specified service is running and false otherwise.
Check for postgres running as part of guards in postgresql recipe

Add PgHelper to organize guards used in the postgresql recipe. With
these changes we skip resources that create dbs and db users if the db
isn't running. If the db _is_ running, then we run checks to make the
resources idempotent.

This change allows the following command sequence to succeed:

    chef-server-ctl stop
    chef-server-ctl reconfigure
    chef-server-ctl start

This is an important pattern for upgrades and for major config
changes, such as changing the port on which a service runs.
Merge branch 'CHEF-4346/rabbitmq-port'
Allow postgresql port to be customized in chef-server.rb config

[CHEF-4235]
Update omnibus-software

Pull in updated nginx config with ipv6 support
Merge branch 'CHEF-4235/postgres-port'