Release notes for 1.12.2
Backport of backfill throttling (fix for #2211).
Passed the mutex_acq parameter through semantic_checking_serializer_t<>::index_write.
adding connection error durability for export
adding connection error durability for import
moving common backup script code into its own file
warning when attempting to join the same peer twice
Changing parent dir fsync from guarantee to warning (to work on VirtualBox shared folders)
Making the message more specific, adding errno to warning
Upgrade packages in the AMI

Review 1425 by @mglukhovsky
Printing err string in addition to errno for portability
Explicitly including utils.hpp
Fix v8 dependency issues in the ubuntu package

Closes #2101
Closes #2261
OTS review by @Tryneus
Release notes for 1.12.3