Remove unused nova.db.api:instance_get_all_by_reservation

Change-Id: I55192773eaa18eb81ffb2b5ec3567b09116b0d1e
Improve output msgs for _compare_result

In case of errors, the messages are now more detailed.
Fixes bug 1133621

Change-Id: I7747d7c4dcaf2199dc55139ee0235f6adca1ad36
Merge "Remove unused nova.db.api:instance_get_all_by_reservation"
Merge "Improve output msgs for _compare_result"