[os] mkdir -p, more tests

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
git: missed var decl

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[subprocess] expose only open interface

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[util] mapObject, extract, dump is improved

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[os] more os.path functions, append_file etc.

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>