PSA: Manual Uprev Conversion Simplification

[Alex Klein]

When converting an existing cros-workon package to only be uprevved manually, you now only need to add CROS_WORKON_MANUAL_UPREV to the unstable (9999) ebuild rather than both the stable and unstable ebuilds. Previously, only adding it to the unstable ebuild would cause an error in the uprev process. We expect this change will make manual uprevs easier to land and easier to review.

The caveat is that the stable ebuild will NOT get CROS_WORKON_MANUAL_UPREV set until a manual uprev is performed, so there are windows where you'd need to check the unstable ebuild to get the correct manual uprev status for the package. If this is a concern for your package (e.g. manual uprevs will be very infrequent, so that window will be large), you can follow up with an uprev, or a manual edit and revbump to add CROS_WORKON_MANUAL_UPREV to the stable ebuild, or even just modify both in one CL as we had to do before.

On behalf of the CrOS Build Team,

Alex