[CTS] Add multi-user B&R base class and managed profile k/v test

1) Creates a base multi-user test class used for setting up and
interacting with other users in the context of backup. Future multi-user
B&R tests will extend from this as well.

2) Creates a test for the backup and restore flow of a key value app in
a managed profile using shared preferences.

Bmgr per-user helpers were added in aosp/874974

Bug: 122305663
Test: atest ManagedProfileKeyValueBackupRestoreHostSideTest
Change-Id: I71f563c0c38c3f5a3cb77eb468ffae64ba78d876
diff --git a/hostsidetests/backup/Android.mk b/hostsidetests/backup/Android.mk
index fd5b3c6..bbe7d47 100644
--- a/hostsidetests/backup/Android.mk
+++ b/hostsidetests/backup/Android.mk
@@ -25,7 +25,7 @@
 
 LOCAL_MODULE := CtsBackupHostTestCases
 
-LOCAL_JAVA_LIBRARIES := cts-tradefed tradefed compatibility-host-util
+LOCAL_JAVA_LIBRARIES := cts-tradefed tradefed compatibility-host-util truth-prebuilt
 
 include $(BUILD_HOST_JAVA_LIBRARY)