OvmfPkg: CI: Use Fedora 35 container (Linux only)

Run the Linux jobs of the OvmfPkg platform CI inside a container,
in the same way the general CI does now. Make use of the default image
specified in the defaults.yml template.

Do not run apt-get in CI jobs to install qemu and gcc dependencies.
Assume the container image provides these.

Use Python from the container image, do not download at runtime.

Signed-off-by: Oliver Steffen <osteffen@redhat.com>
Acked-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Michael Kubacki <michael.kubacki@microsoft.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Chris Fernald <chfernal@microsoft.com>

OvmfPkg/PlatformCI/.azurepipelines/Ubuntu-GCC5.yml

@@ -180,6 +180,8 @@ jobs:
     pool:
       vmImage: $(vm_image)
 
+    container: ${{ variables.default_linux_image }}
+
     steps:
     - template: ../../../.azurepipelines/templates/platform-build-run-steps.yml
       parameters:
@@ -190,8 +192,4 @@ jobs:
         build_file: $(Build.File)
         build_flags: $(Build.Flags)
         run_flags: $(Run.Flags)
-        usePythonVersion: ${{ variables.default_python_version }}
-        extra_install_step:
-        - bash: sudo apt-get install qemu
-          displayName: Install qemu
-          condition: and(gt(variables.pkg_count, 0), succeeded())
+        usePythonVersion: '' # use Python from the container image