Following the Gerrit upgrade, the release team lost the "PTL+1" column
in the release dashboard, which made it convenient dte screen
ready-to-process changes.
New gerrit only displays "required" labels. This change makes PTL+1
blocking in case the lowest negative value is selected (AnyWithBlock),
while defining a negative value that nobody can actually set.
Change-Id: Idbf614be4b88db56258ed3b0e7725b581196a6fb
de372833c5