tests/libqtest: Fix description of qtest_vinitf() and qtest_initf()

These functions are convenience wrappers of qtest_init() and not of
qtest_start().
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190513154759.24973-1-thuth@redhat.com>
Signed-off-by: NThomas Huth <thuth@redhat.com>

tests/libqtest.h

@@ -29,7 +29,7 @@ extern QTestState *global_qtest;
  * @fmt...: Format for creating other arguments to pass to QEMU, formatted
  * like sprintf().
  *
- * Convenience wrapper around qtest_start().
+ * Convenience wrapper around qtest_init().
  *
  * Returns: #QTestState instance.
  */
@@ -41,7 +41,7 @@ QTestState *qtest_initf(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
  * like vsprintf().
  * @ap: Format arguments.
  *
- * Convenience wrapper around qtest_start().
+ * Convenience wrapper around qtest_init().
  *
  * Returns: #QTestState instance.
  */