oeqa/runtime: Add case, context and loader classes for runtime testing
This adds OERuntimeTestCase, OERuntimeTestContext, and OERuntimeTestLoader
to be used for runtime testing.
As expected there are some changes in runtime context:
- Adds the target to be used for runtime testing, the default
is a SSH connection to the device under test running a OE image.
- Runtime context requires image manifest because several
tests are skipped if a package is missing or installed.
- Several tests require the output of the ps command and it changes
its output and arguments if busybox o procps is installed, so the
case must use the correct ps command.
