Install the proper requirements for pysaml2 in the trial test runners.

.gitignore

@@ -0,0 +1 @@
+.idea/

synapse/pipeline.yml

@@ -1,3 +1,15 @@
+# This is just a dummy entry (the `x-yaml-aliases` key is not an official pipeline key, and will be ignored by BuildKite)
+# that we use only to store YAML anchors (`&xxx`), that we plan to use and reference later in the YAML file (using `*xxx`)
+# without having to copy/paste the same values over and over.
+# Note: keys like `agent`, `env`, … used here are totally arbitrary; the only point is to define various separate `&xxx` anchors there.
+#
+x-yaml-aliases:
+  commands:
+    - &trial_setup |
+      # Install additional packages that are not part of buildpack-deps / python images.
+      apt-get update && apt-get install -y xmlsec1
+      python -m pip install tox
+
 env:
   COVERALLS_REPO_TOKEN: wsJWOby6j0uCYFiCes3r0XauxO27mx8lD
 
@@ -114,7 +126,7 @@ steps:
 
   - label: ":python: 3.5 / SQLite"
     command:
-      - "python -m pip install tox"
+      - *trial_setup
       - "tox -e py35,combine"
     env:
       TRIAL_FLAGS: "-j 2"
@@ -137,7 +149,7 @@ steps:
 
   - label: ":python: 3.6 / SQLite"
     command:
-      - "python -m pip install tox"
+      - *trial_setup
       - "tox -e py36,combine"
     env:
       TRIAL_FLAGS: "-j 2"
@@ -160,7 +172,7 @@ steps:
 
   - label: ":python: 3.7 / SQLite"
     command:
-      - "python -m pip install tox"
+      - *trial_setup
       - "tox -e py37,combine"
     env:
       TRIAL_FLAGS: "-j 2"
@@ -189,7 +201,8 @@ steps:
       PYTHON_VERSION: "3.5"
       POSTGRES_VERSION: "9.5"
     command:
-      - "bash -c 'python -m pip install tox && python -m tox -e py35-postgres,combine'"
+      - *trial_setup
+      - "python -m tox -e py35-postgres,combine"
     plugins:
       - matrix-org/download#v1.1.0:
           urls:
@@ -218,7 +231,8 @@ steps:
       PYTHON_VERSION: "3.7"
       POSTGRES_VERSION: "11"
     command:
-      - "bash -c 'python -m pip install tox && python -m tox -e py37-postgres,combine'"
+      - *trial_setup
+      - "python -m tox -e py37-postgres,combine"
     plugins:
       - matrix-org/download#v1.1.0:
           urls:
@@ -247,7 +261,8 @@ steps:
       PYTHON_VERSION: "3.8"
       POSTGRES_VERSION: "12"
     command:
-      - "bash -c 'python -m pip install tox && python -m tox -e py38-postgres,combine'"
+      - *trial_setup
+      - "python -m tox -e py38-postgres,combine"
     plugins:
       - matrix-org/download#v1.1.0:
           urls: