Add Restore Mode to stop api calls while restoring

The main goal of this PR is to prevent data loss
during the different steps of the restore process.
This will be used by restore once it lands.
This is the basic required functionality for this
API server mode.
Following a feaure implemented for Upgrade, an
api root server that can selectively allow API
commands depending on the Restore step we are
running.
When we are preparing a restore: that includes
uploading files if required for instance, the
API will only accept Client.Restore to be
triggered in order to avoid data loss when the
restore runs.
When Restore is running no calls will be allowed
since state server will be down.
Core changes to store tools in state
Search, download and cache tools from public/configured tools sources

FindTools will now search simplestreams unless an exact match is
being performed and that is found in toolstorage. Tools found in
toolstorage will take precedence over those in simplestreams.

If a tools version is requested for download and it is not in
toolstorage already, the API server will search for it in simplestreams,
download it, and cache it in toolstorage before returning it to
the client.

Also, we now once again (as in 1.20) only clone tools on upload if
requested. We will drop the "AddToolsAlias" function from toolstorage.
cmd/jujud: clone tools, don't alias metadata
Fix apiserver tools serving
Fix tests
Remove DisplayName option

Remove the option to set an environ user's display name from the
AddEnvirionmentUser function. Update call sites and expected test
results.
Merge pull request #696 from wallyworld/keep-broken-part-2

Do not stop bootstrap instance on error if keep-broken flag is true

Fixes: https://bugs.launchpad.net/bugs/1365772

The --keep-broken flag was added for 1.20.7 and it did stop the environment from being destroyed on a failed bootstrap, but did not stop the bootstrap instance from being stopped. This PR adds in the extra logic to do that.
cmd/jujud: don't redirect bootstrap-state logs

Redirecting bootstrap logs breaks bootstrap error reporting.

Fixes https://bugs.launchpad.net/juju-core/+bug/1366650
cmd/jujud: log stack trace on panic
cmd/jujud: read tools into memory before adding to storage
s/ToolsStorager/ToolsStorageGetter/g
state/toolstorage: remove AddToolsAlias

We're no longer aliasing, just adding cloned
tarballs for each version, which will be
de-duplicated by managed storage. This will
simplify the removal of old tarballs from
storage.
Fix tests
Merge pull request #701 from wallyworld/keep-broken-part-2-trunk

Merge pull request #696 from wallyworld/keep-broken-part-2

Port from 1.20

Do not stop bootstrap instance on error if keep-broken flag is true

Fixes: https://bugs.launchpad.net/bugs/1365772

The --keep-broken flag was added for 1.20.7 and it did stop the environment from being destroyed on a failed bootstrap, but did not stop the bootstrap instance from being stopped. This PR adds in the extra logic to do that.
Merge branch 'master' of https://github.com/juju/juju into remove-display-name
Merge pull request #691 from waigani/remove-display-name

Remove DisplayName option

Remove the option to set an environ user's display name from the
AddEnvirionmentUser function. Update call sites and expected test
results.
Remove AddAdminUser and create the user when the environment is created.
Merge pull request #695 from howbazaar/remove-add-admin-user

Remove AddAdminUser and create the user when the environment is created.

The admin user is now created when the environment is created as part of the state initialization function.
The admin user also has an environment user record added for the initial environment.
apiserver/common: address review comments

- Fix comments
- Bail early if AllMetadata returns an error
- Improve FindTools (API server) coverage