libqtest: Replace qtest_startf() by qtest_initf()

qtest_init() creates a new QTestState, and leaves @global_qtest alone.
qtest_start() additionally assigns it to @global_qtest, but
qtest_startf() additionally assigns NULL to @global_qtest.  This makes
no sense.  Replace it by qtest_initf() that works like qtest_init(),
i.e. leaves @global_qtest alone.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180806065344.7103-23-armbru@redhat.com>
diff --git a/tests/libqtest.c b/tests/libqtest.c
index 2f81bc6..a0d4479 100644
--- a/tests/libqtest.c
+++ b/tests/libqtest.c
@@ -259,24 +259,23 @@
     return s;
 }
 
-QTestState *qtest_vstartf(const char *fmt, va_list ap)
+QTestState *qtest_vinitf(const char *fmt, va_list ap)
 {
     char *args = g_strdup_vprintf(fmt, ap);
     QTestState *s;
 
-    s = qtest_start(args);
+    s = qtest_init(args);
     g_free(args);
-    global_qtest = NULL;
     return s;
 }
 
-QTestState *qtest_startf(const char *fmt, ...)
+QTestState *qtest_initf(const char *fmt, ...)
 {
     va_list ap;
     QTestState *s;
 
     va_start(ap, fmt);
-    s = qtest_vstartf(fmt, ap);
+    s = qtest_vinitf(fmt, ap);
     va_end(ap);
     return s;
 }