qemuargv2xmltest: Fix caps loading in VPATH build

Broken by v4.7.0-rc1-9-g6700062f.
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>

tests/qemuargv2xmltest.c

@@ -159,7 +159,7 @@ mymain(void)
     do { \
         virQEMUCapsPtr qemuCaps; \
         qemuCaps = qemuTestParseCapabilitiesArch(VIR_ARCH_X86_64, \
-                                                 "qemucapabilitiesdata/caps_2.12.0." arch ".xml"); \
+                                                 abs_srcdir "/qemucapabilitiesdata/caps_2.12.0." arch ".xml"); \
         if (virFileCacheInsertData(driver.qemuCapsCache, \
                                    "/usr/bin/qemu-system-" arch, \
                                    qemuCaps) < 0) \