xenconfig: support bios=ovmf xl.cfg

Add support to xenconfig for conversion of xl.cfg(5) bios config
to/from libvirt domXml <loader> config. SeaBIOS is the default
for HVM guests using upstream QEMU. ROMBIOS is the default when
using the old qemu-dm. This patch allows specifying OVMF as an
alternate firmware.

Example xl.cfg:
  bios = "ovmf"

Example domXML:
  <os>
    ...
    <loader readonly='yes' type='pflash'>/usr/lib/xen/boot/ovmf.bin</loader>
  </os>

Note that currently Xen does not support a separate nvram for
non-volatile variables.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>

tests/testutils.c

@@ -718,6 +718,22 @@ virTestCompareToFile(const char *strcontent,
     return ret;
 }
 
+/*
+ * @param strcontent: String input content
+ * @param strsrc: String source to compare strcontent against
+ */
+int
+virTestCompareToString(const char *strcontent,
+                       const char *strsrc)
+{
+    if (STRNEQ_NULLABLE(strcontent, strsrc)) {
+        virTestDifference(stderr, strcontent, strsrc);
+        return -1;
+    }
+
+    return 0;
+}
+
 static void
 virTestErrorFuncQuiet(void *data ATTRIBUTE_UNUSED,
                       virErrorPtr err ATTRIBUTE_UNUSED)