[0.12.0] [xenial] Create test plans and QA matrix

[eloquence]

In preparation for SecureDrop 0.12.0 and as part of Xenial support (#3204), we will need to prepare the following documents:

• a 0.12.0 test plan for instances upgrading from 0.11.1, similar to the 0.11.0 test plan
• a standard release QA matrix, similar to the 0.11.0 release QA matrix
• a test plan and QA matrix specifically for a freshly installed version of SecureDrop 0.12.0 on Ubuntu 16.04 per the revised documentation ([xenial] Update the install guide to account for the use of Xenial instead of Trusty as the server base OS #4103)
• a test plan and QA matrix specifically for a SecureDrop 0.12.0 installation upgraded from Ubuntu 14.04 to Ubuntu 16.04 per the upgrade docs ([xenial] Document upgrade process #4057)

We do not need to test installation of SecureDrop 0.12.0 on Trusty, as this option will not be supported.

Part of #3204 and the 0.12.0 release epic.

[zenmonkeykstop]

There will probably be 2 upgrade scenarios to test here:

• testing Xenial after an upgrade in place.
• testing Xenial after a backup-install-restore upgrade.

[heartsucker]

See the wiki post for the current test plan.

[heartsucker]

@eloquence I think this ticket is covered by the release ticket, wiki entry, and QA spreadsheet. I recommend we close this.

[redshiftzero]

We can close this and move on to other tasks - each scenario above is written out in row 2 of the (single) QA matrix. Users should add their QA reports as new columns in the QA matrix, along with a report on the ticket itself.