Allow user to set ara_report_executable

Default to 'ara' for the executable but also allow for a user to use the
full path if they want.

Change-Id: I26aac0d25f071b65b20f97622836abf56e65cebc
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

roles/ara-report/README.rst

@@ -57,3 +57,8 @@ If ARA is enabled, generates a report or saves a copy of the ARA database.
 
    When report_type is 'html' directory where the HTML report will be generated.
    When report_type is 'database', directory where the database is saved.
+
+.. zuul:rolevar:: ara_report_executable
+   :default: ``ara``
+
+   Path to ara executable.

roles/ara-report/defaults/main.yaml

@@ -24,3 +24,5 @@ ara_report_path: 'ara'
 
 # When report_type is 'html', whether to compress the ARA HTML output or not
 ara_compress_html: true
+
+ara_report_executable: ara

roles/ara-report/tasks/main.yaml

@@ -1,6 +1,6 @@
 - block:
     - name: Check that ARA is installed
-      command: bash -c "type -p ara"
+      command: bash -c "type -p {{ ara_report_executable }}"
       ignore_errors: yes
       register: ara_installed
 
@@ -48,7 +48,7 @@
     # Always generate (true), never (false) or only on failure ('failure')
     # Additionally cover for edge cases where zuul_success might be undefined
     - name: Generate ARA HTML output
-      command: "ara generate html {{ final_ara_report_path }}"
+      command: "{{ ara_report_executable }} generate html {{ final_ara_report_path }}"
       environment:
         ARA_DATABASE: "sqlite:///{{ ara_database_path }}"
       when: ara_report_run | bool or