Signed-off-by: Cleber Rosa <[email protected]>

The exec-test and tap resolvers share the same code that verifies the
condition of the reference given being an executable file.

This would be enough to consolidate them into a single method, but
there's going to be a third users of the same check, so there's more
reason for that yet.

Signed-off-by: Cleber Rosa <[email protected]>

This resolver is somewhat of a hybrid between the "exec-test" and the
"runnables-recipe" resolvers.

It runs an executable, and attempts to read from its STDOUT content
that will be treated as runnables-recipe JSON content.  If that
succeeds, the content will be returned as test resolutions.  This is
useful for executable tests or test generators that will output the
tests dinamically.

Signed-off-by: Cleber Rosa <[email protected]>

This adds support for used defined arguments to be passed while
running the executables that will generate the runnables recipe JSON
content.

It gives the opportunity for either calling the executables with a
particular option that will output the runnables (instead of other
action), or tweaking the type of runnables that will be generated.

Signed-off-by: Cleber Rosa <[email protected]>