tests: Add new "real-life" test suit

The intention is to put here tests, that check how real apps
work. Initially I test that make -j4 works. This test is very
basic (uses sleep to wait for make to fork everybody) and a
syntetic .c file (quite big though).

Extend and use.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>