Added support for ramdisk-type elements in tests/test_functions.bash
Elements are distinguished by element-type file in a test element.
Note that ironic-agent ramdisk is built with disk-image-create.
Change-Id: I4759859e7f3c004c2d00e7318729602e6c3c4d95
Adding a test function which allows us to use elements to perform
element-specific tests. In order for this to work sanely, also adding
some configuration to our break system so we can assert on negative
tests.
Also adding a test for apt-sources to verify this code actually works.
Change-Id: I378a74255010eca192f5766b653f8a42404be5ea