tests: add a local test for guest agent

tests: add a local test for guest agent

Add some local guest agent tests, as it is better than nothing, only
when CONFIG_POSIX (using unix sockets).

With the QGA_TEST_SIDE_EFFECTING environment variable, it will include
tests with side effects, such as freezing/thawing the FS or changing the
time.

(a better test would involve a managed VM (or container), but it might
be better to leave that off to autotest/avocado)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
* use mkdtemp() in placeof g_mkdtemp() for glib 2.22 compat
* drop redundant/conflicting compat defines for
  g_assert_{true,false}, since glib-compat has them now.
* build fixes for OSX: use PRId64 instead of glib formats, drop
  g_spawn_default usage for glib compat
* assert connect_qga() doesn't fail
* only enable test-qga for linux hosts
* allow get-memory-block-info* to fail
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>