libqos: Track QTestState with QPCIBus

libqos: Track QTestState with QPCIBus

When initializing a QPCIBus, track which QTestState the bus is
associated with (so that a later patch can then explicitly use
that test state for all communication on the bus, rather than
blindly relying on global_qtest).  Update the initialization
functions to take another parameter, and update all callers to
pass in state (for now, most callers get away with passing the
current global_qtest as the current state, although this required
fixing the order of initialization to ensure qtest_start() is
called before qpci_init*() in rtl8139-test, and provided an
opportunity to pass in the allocator in e1000e-test).

Touch up some allocations to use g_new0() rather than g_malloc()
while in the area, and simplify some code (all implementations
of QOSOps provide a .init_allocator() that never fails).

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
[thuth: Removed hunk from vhost-user-test.c that is not required anymore,
 fixed conflict in qtest_vboot() and adjusted qpci_init_pc() in sdhci-test]
Signed-off-by: Thomas Huth <thuth@redhat.com>