Add ability to pass environment to gate runner from job

Introduces an ability to pass custom environment that
has the highest precedence from job definition for
airshipctl-gate-runner playbook, e.g.:

job:
  name: test-job
  playbook: run: playbooks/airshipctl-gate-runner.yaml
  vars:
    job_environment:
      FOO: BAR

Defined environment variables complete/replace default playbook variables.

Change-Id: Ib11480068141315126a80f3952b6882cdb7439ae
Signed-off-by: Andrii Ostapenko <andrii.ostapenko@att.com>

roles/airshipctl-run-script/tasks/main.yaml

@@ -10,14 +10,21 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+- name: Set default_zuul_dir
+  set_fact:
+    default_zuul_dir: "{{ ansible_user_dir }}/{{ zuul.project.src_dir }}"
+
+- name: Set env facts
+  set_fact:
+    local_environment:
+      AIRSHIP_CONFIG_PHASE_REPO_URL: "{{ remote_work_dir | default(local_src_dir) | default(default_zuul_dir) }}"
+      SITE: "{{ site | default('test-site') }}"
+    job_environment: "{{ job_environment | default({}) }}"
+
 - name: "Run script {{ gate_script_path }}"
+  environment: "{{ local_environment | combine(job_environment) }}"
   shell: |
     set -xe;
     {{ gate_script_path }}
   args:
     chdir: "{{ zuul.project.src_dir }}"
-  vars:
-    default_zuul_dir: "{{ ansible_user_dir }}/{{ zuul.project.src_dir }}"
-  environment:
-    AIRSHIP_CONFIG_PHASE_REPO_URL: "{{ remote_work_dir | default(local_src_dir) | default(default_zuul_dir) }}"
-    SITE: "{{ site | default('test-site') }}"