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>
diff --git a/ansible/group_vars/all.yml b/ansible/group_vars/all.yml
index dc40238c..8536395 100755
--- a/ansible/group_vars/all.yml
+++ b/ansible/group_vars/all.yml
@@ -113,7 +113,7 @@
 
 # Main Helm chart to install
 # e.g. app_helm_chart_name: onap
-app_helm_chart_name: "{{ app_name }}"
+app_helm_chart_name:
 
 # Targets for helm charts repository build
 # e.g. for ONAP Casablanca
@@ -137,7 +137,7 @@
 
 # Optional application custom Ansible roles name for pre and post install logic.
 # Location of additional custom roles is defined in ansible.cfg with roles_path.
-# e.g. application_pre_install_role: "{{ app_name }}-patch-role"
+# e.g. application_pre_install_role: "my-pre-install-role"
 application_pre_install_role:
 application_post_install_role: