EUCA-5069: initial cut at refactoring into migration_handler() function
Changed doMigrateIntances() to take an action parameter.

Finished move of migration logic from refresh_instances() to
migration_handler().

Implements EUCA-5069.
EUCA-5069: add migration credentials & timestamp to ncInstance struct
Updated NCclient help
Added self-timeout/rollback of source nodes awaiting migration.

Added configurable migration-ready timeout (NC_MIGRATION_READY_THRESHOLD)
with 15-minute default.

Implements EUCA-5069.
Merge remote-tracking branch 'origin/team/evac' into dev/juphoff/evac
Merge remote-tracking branch 'origin/team/evac' into testing