All test/TEST* but TEST-02-CRYPTSETUP share the same check_result_qemu()
and test_cleanup(), so move them into test_functions and only override
them in TEST-02-CRYPTSETUP.

Also provide a common test_run() which by default assumes that both QEMU
and nspawn tests are run. Particular tests which don't support either
need to explicitly opt out by setting $TEST_NO_{QEMU,NSPAWN}. Do it this
way around to avoid accidentally forgetting to opt in, and to encourage
test authors to at least always support nspawn.

This makes nspawn tests symmetric with run_qemu() which also exits with 1 if
QEMU is not available.

It tries to find a suitable QEMU binary and will use KVM if present.
We can now configure QEMU from outside with 4 variables :
  - $QEMU_BIN : path to QEMU's binary
  - $KERNEL_APPEND : arguments appended to kernel cmdline
  - $KERNEL_BIN : path to a kernel
    Default /boot/vmlinuz-$KERNEL_VER
  - $INITRD : path to an initramfs
    Default /boot/initramfs-${KERNEL_VER}.img
  - $QEMU_SMP : number of CPU simulated by QEMU.
    Default 1

(from Alexander Graf's script: http://www.spinics.net/lists/kvm/msg72389.html)

- fix typo
- use compiled systemd-nspawn
- drop --capability=... from systemd-nspawn invocation, is is the default now
- simplify sudo make invocations

Add a test case for job merging with --ignore-dependencies.

test.sh is copied from TEST-01-*, only lightly modified (this
should be refactored better in the future).
test-jobs.sh is the core of this test.

Tests can use the same testsuite.target.
Add end.service to call poweroff instead of doing it from ExecStopPost
where it may be skipped on failure of ExecStart.

"systemctl poweroff" called from testsuite.service will cause this unit
itself to stop. To avoid deadlock, the call must not be synchronous.

$ cd test
$ sudo make check

will run all tests in the TEST-* subdirectories

$ cd test/TEST-01-BASIC
$ sudo make clean setup run

will run the different stages of the test for debugging purposes