selftest/recipetool: Add tests for branch parameter and srcbranch option

The recipetool support two ways to pass a branch and fallback to master
if no branch is defined. Add tests for default branch, branch parameter
and srcbranch option.

Signed-off-by: Stefan Herbrechtsmeier <stefan.herbrechtsmeier@weidmueller.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>