Refine application_pre_install_role variable usage

Refine application_pre_install_role variable usage

As 'application_pre_install_role' variable set in
config/application_configuration.yml must stay in
sync with patch role directory name defined in
package.conf under APP_CONFIGURATION variable, it's
name shall stay under complete user control without
any variable as part of it's name.

App_helm_build_targets list and app_helm_chart_name
should default to 'onap' in application_configuration.yml
as customizing them isn't supported at the moment.

Also fixed some wording in comments/docs in relevant
files.

Change-Id: I82b6dd519fbc3426739a11fac1e02eb495a668c0
Issue-ID: OOM-1697
Signed-off-by:  Bartek Grzybowski <b.grzybowski@partner.samsung.com>