Rewrite how we abandon sessions

The original code is flawed in that `pm install-abandon` only abandons
the 1st session returned by `pm get-stagedsessions ...`.

1. move AbandonSessionsRule to be shared by multiple host tests
2. use AbandonSessionsRule to do the job

Bug: 160754072
Test: StagedInstallInternalTest
Change-Id: Ib7b32fbd7b1133ac6a8e6782234a4fe2c5a782bd