Utils: Add get_temp_dir() function

Signed-off-by: Tomas Hozza <thozza@redhat.com>
Settings: Add REBASE_HELPER_PREFIX variable

Signed-off-by: Tomas Hozza <thozza@redhat.com>
BuildHelper: Finished MockBuildTool, Almost finished RpmbuildBuildTool

Signed-off-by: Tomas Hozza <thozza@redhat.com>