Allow specifying multiple objects in YAML source/handler files

Support both single-object and lists when reading handlers and sources
from YAML files in a directory.
3 jobs for master in 2 minutes and 2 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build Src
passed #8792
build:src

00:00:21

 
  Build Pkg
passed #8793
build:pkg

00:01:14

 
  Upload
passed #8794
upload:pkg

00:00:26