Adds a new job CI
build linux ubuntu perf which is run on master only and which runs benchmarks serially (excluding large ones and also excluding PETSc-based benchmarks).
Builds can be seen in CDash.
When viewing a specific build there is the column "Time Status" which shows a Warning if a tests runtime differs much from previous runs. For that to work we need some more builds.
In CDash there is also the possiblity to get email notifications on such things but I have not got it to work yet..