Fix error message in pre_live_migration.

We are using locals() to reference a variable which doesn't exist
in this error message. Also rename the instance variable while I
am here to be more consistent with other uses.

Resolves bug 1164072.

Change-Id: I96f5e2a81ac2e97181c3e87df83e19b381f4bcd2
(cherry picked from commit 676b16bfe5ff41eb28d782c888c17dae6bdff76a)
Remove unnecessary db call in scheduler driver live-migration code

When the scheduler selects a destination host for live-migration, a db
call is made to get instance_type info for the instance. To avoid the
db call, this should instead call instance_types.extract_instance_type
on the instance.

Resolves bug 1167811.

Change-Id: I2025fdf1d34e70158360ff71e8545c8e3bc6bc80
(cherry picked from commit 5f68160354d240b191bcbaabca7d3c0684758cc6)
Merge "Fix error message in pre_live_migration." into stable/grizzly
Merge "Remove unnecessary db call in scheduler driver live-migration code" into stable/grizzly