Build names containing branch and commit.

- in main multijob inject a shell script just after git clone that
  produce a properties file with build name
- in all jobs set build name to the name from properties file + its own build number
- put common stuff (build name, node, workspace) into default 'flow123d-build'

Gotchas:
- need to use double braces in Jenkins job builder YAML files, since singel braces are used for template parameter expansion
- defaults are applied before other processing comes, so thay can contain template placeholders
Merge branch 'master' into JB_test_branch