[SRU] Please SRU py-macaroon-bakery 1.2.1

[Andres Rodriguez]

[Impact]
* py-macaroon-bakery 1.2.1 has several changes and fixes that allow third party software to integrate with Candid for macaroon based authentication. Without this version, users are unable to integrate their software with Candid.

* As part of supporting external authentication and RBAC in MAAS, the newer version is required to fix a few issues, such as

 - https://bugs.launchpad.net/maas/+bug/1786830 (allowing using hostnames without domain for the candid host) which is fixed here: https://github.com/go-macaroon-bakery/py-macaroon-bakery/pull/54

 - fix for https://github.com/go-macaroon-bakery/py-macaroon-bakery/issues/57, which happens when MAAS uses the bakery client to talk to RBAC.

[Test Case]

Without this version:
1. Install MAAS
2. Install Candid and configure it with a location like 'http://<hostname>:8081'
3. Configure MAAS w/ Candid
4. Attempt authentication -> it will fail.

With this version:
1. Install MAAS
2. Install Candid and configure it with a location like 'http://<hostname>:8081'
3. Configure MAAS w/ Candid
4. Attempt authentication -> it will suceed.

[Regression potential]
* Regession potential is low, as changes between 1.1.3 and 1.2.1 are only related to bugfixes.