Use wwan-automated nested part in SRU test plan (bugfix) (#1499)

Use wwan-automated nested part in SRU test plan

Replace mobilebroadband-cert-automated with wwan-automated nested part,
as the wwan-automated test plan includes better coverage for
WWAN-related tests.

Add after-suspend-wwan-automated counterpart to make sure there are no
issues with WWAN after resuming from suspend.

This is a follow-up to work done by QA in the certification-client
desktop test plans (see #821)

Fix CER-2738

providers/sru/units/sru.pxu

@@ -54,7 +54,7 @@ nested_part:
     mediacard-cert-automated
     mediacard-automated
     memory-automated
-    mobilebroadband-cert-automated
+    wwan-automated
     ethernet-cert-automated
     networking-cert-automated
     optical-cert-automated
@@ -68,6 +68,7 @@ nested_part:
     before-suspend-reference-cert-full
     # suspend point
     after-suspend-reference-cert-full
+    after-suspend-wwan-automated
     after-suspend-touchscreen-cert-automated
     after-suspend-wireless-cert-automated
     # The following tests should run BEFORE the automated tests. The reboot and