This patch modifies all example tests to use the new API. It uses the
default path, which is `*`, which matches the mux-entry paths ONLY.
In order to get the values it's necessarily to inject the YAML files
into the mux-entry path, by default `/test`, eg:

    avocado run sleeptest -m /test:examples/tests/sleeptest.py.data/
    sleeptest.yaml

It might seen as a bit more complicated to execute, but it's definitely
easier for maintaining and combining existing YAML files. To execute
matrix of tests you simply inject them into 2 different `/test` children,
eg: `-m /test/by_length:lengths.yaml /test/by_method:methods.yaml`.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>