Update heat content for Juno

I updated the heat content in the installation guide for Juno
as follows:

1) Restructured procedures to match other chapters.
2) Removed MySQL references.
3) Added step to load admin credentials prior to keystone
   steps.
4) Added region to endpoints.
5) Added note about verbose mode.
6) Explictly installed python-heatclient package.
7) Removed 'logdir' workaround for Ubuntu.
8) Changed RHEL/CentOS/Fedora to use systemd init scripts.
9) Changed openSUSE to use systemd init scripts.
10) Fixed other minor issues.

I tested the contents of this patch on RHEL, CentOS, Fedora,
and Ubuntu.

Change-Id: Ia35dd4adfd89c34a2a1574510a430737c938a159
Merge "Update heat content for Juno"