* Edits to apply organizational improvements made in the HAWQ version, using consistent realm and domain names, and testing that procedures work.

* Convert tasks to topics to fix formatting. Clean up pg_ident.conf topic.

* Convert another task to topic

* Remove extraneous tag

* Formatting and minor edits

* - added $ or # prompts for all code blocks
- Reworked section "Mapping Kerberos Principals to Greenplum Database Roles" to describe, generally, a user's authentication process and to more clearly describe how principal name is mapped to gpdb name.

* - add krb_realm auth param

- add description of include_realm=1 for completeness

* DOCS: removing DDBoost info from OSS build

* DOCS: Removing RHEL 5 reference

* adding psql example to kerberos linux client doc

* removing client/loader maps from main .ditamap

* removing client tool guides from repo

* moving linux kerberos client instructions to dedicated topic, and placing it parallel with existing windows topic

* removing map and dita files for connectivity package, which is no longer provided

* removing more references to connectivity packages; conditionalizing postgres odbc/jdbc vs datadirect drivers for oss/pivotal audiences

* adding .ditaval for handling pivotal conditions; [ci skip]

* relocating pivotal ditaval