Perform userdata backup for all matching rollbacks

Currently, the snapshot of userdata is performed by traversing
the list of rollbacks and matching based on the package name, returning
once a match is found and the userdata has been backed up. There may
be cases where multiple rollbacks match this package name, so we should
not return until we have checked all rollbacks.

Bug: 134485920
Test: atest RollbackTest
Test: atest StagedRollbackTest
Change-Id: If6051ba11b2163e282e7bb61ff02e669ba1079ab