Optionally install uStreamer from Debian package (#110)

Related #100

This PR only builds uStreamer from source if a uStreamer Debian package
is not provided. This will allow TinyPilot to specify a uStreamer Debian
package and avoid building uStreamer from source on every
install/update.

I've [tested these changes in
CI](https://app.circleci.com/pipelines/github/tiny-pilot/ansible-role-ustreamer/371/workflows/f85d89d6-bf24-40e7-868b-692299e6c38e/jobs/962?invite=true#step-104-396)
via
179fe04.

I've also tested these changes on device via a [scratch TinyPilot Pro
PR](tiny-pilot/tinypilot-pro#908).

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defaults/main.yml

@@ -1,4 +1,8 @@
 ---
+# Specifies the filesystem path or URL of a Debian package that installs
+# uStreamer.
+ustreamer_debian_package_path: null
+
 ustreamer_repo: https://github.com/pikvm/ustreamer.git
 ustreamer_repo_version: master
 

tasks/main.yml

@@ -113,6 +113,11 @@
     name: "{{ ustreamer_packages }}"
     state: present
 
+- name: install uStreamer Debian package
+  apt:
+    deb: "{{ ustreamer_debian_package_path }}"
+  when: ustreamer_debian_package_path != None
+
 - name: create uStreamer folder
   file:
     path: "{{ ustreamer_dir }}"
@@ -125,6 +130,7 @@
     # to set the correct directory ownership that allows git to sync.
     # Issue: https://github.com/tiny-pilot/tinypilot/issues/963
     - molecule-idempotence-notest
+  when: ustreamer_debian_package_path == None
 
 - name: get uStreamer repo
   # Don't escalate privileges because only the directory owner can use git.
@@ -139,6 +145,7 @@
     # idempotency test on the previous task that allows git to sync.
     # Issue: https://github.com/tiny-pilot/tinypilot/issues/963
     - molecule-idempotence-notest
+  when: ustreamer_debian_package_path == None
 
 # We always need to clean and build uStreamer to ensure that the uStreamer
 # service is in sync with its dependencies installed on the device.
@@ -149,6 +156,7 @@
     target: clean
   tags:
     - molecule-idempotence-notest
+  when: ustreamer_debian_package_path == None
 
 - name: build uStreamer
   make:
@@ -159,6 +167,7 @@
     - restart uStreamer
   tags:
     - molecule-idempotence-notest
+  when: ustreamer_debian_package_path == None
 
 - name: fix uStreamer folder permissions
   file:
@@ -212,7 +221,7 @@
     dest: "{{ ustreamer_janus_plugins_dir }}"
   notify:
     - restart Janus
-  when: ustreamer_install_janus
+  when: ustreamer_debian_package_path == None and ustreamer_install_janus
 
 - name: install uStreamer launcher
   import_tasks: install_launcher.yml