State: Migrate instanceId

Add an upgrade step to migrate the depricated "instanceid" machine
field into "instanceid" in the instanceData doc.
fix conflicts
State, upgrade step: Add EnvUUID to Sequence doc IDs

Adds an upgrade step to add the EnvUUID to sequence doc IDs.
Add a --download option to "juju backups create".
Add a --filename option.
Drop superfluous if statement.
Use a more meaningful (in help) "default" for --filename.
Add a recommendation to download backups.
Fix tests.
Merge branch 'master' of https://github.com/juju/juju into migrate-instanceid
Merge pull request #1002 from ericsnowcurrently/backups-create-download

Add --download and --filename options to "juju backups create".
Merge pull request #916 from waigani/migrate-instanceid

State: Migrate instanceId

Add an upgrade step to migrate the depricated "instanceid" machine
field into "instanceid" in the instanceData doc.
Merge branch 'master' of https://github.com/juju/juju into migrate-sequences
Merge branch 'master' of https://github.com/juju/juju into migrate-sequences
Merged 1.21 upgrade steps into one list

Without this, upgrade steps really end up running in the wrong
order. Steps like the machine and instanceData env UUID migrations
really need to go first.

This change solves the immediate issue. A future change will tidy
this up so that the steps can be assigned against 1.21 final instead
of alpha1.
Merge pull request #973 from waigani/migrate-sequences

State, upgrade step: Add EnvUUID to Sequence doc IDs

Adds an upgrade step to add the EnvUUID to sequence doc IDs.
Merge pull request #1008 from mjs/merge-121-upgrade-steps

Merged 1.21 upgrade steps into one list

Without this, upgrade steps really end up running in the wrong order. Steps like the machine and instanceData env UUID migrations really need to go first.

This change solves the immediate issue. A future change will tidy this up so that the steps can be assigned against 1.21 final instead of alpha1.
state: added State.EnvironUUID and use it everywhere

EnvironTag().Id() is commonly used to get the environment UUID. A
EnvironUUID method has been added to provide a more direct and easier
to read way of obtaining the environment UUID.