Look in /usr/libexec for the qemu-kvm binary.

On RHEL-5 the qemu-kvm binary is located in /usr/libexec.
To reduce confusion for people trying to run upstream libvirt
on RHEL-5 machines, make the qemu driver look in /usr/libexec
for the qemu-kvm binary.

To make this work, I modified virFindFileInPath to handle an
absolute path correctly.  I also ran into an issue where
NULL was sometimes being passed for the file parameter
to virFindFileInPath; it didn't crash prior to this patch
since it was building paths like /usr/bin/(null).  This
is non-standard behavior, though, so I added a NULL
check at the beginning.
Signed-off-by: NChris Lalancette <clalance@redhat.com>

src/qemu/qemu_conf.c

@@ -804,7 +804,8 @@ qemudCapsInitGuest(virCapsPtr caps,
     if (STREQ(info->arch, hostmachine) ||
         (STREQ(hostmachine, "x86_64") && STREQ(info->arch, "i686"))) {
         if (access("/dev/kvm", F_OK) == 0) {
-            const char *const kvmbins[] = { "qemu-kvm", /* Fedora */
+            const char *const kvmbins[] = { "/usr/libexec/qemu-kvm", /* RHEL */
+                                            "qemu-kvm", /* Fedora */
                                             "kvm" }; /* Upstream .spec */
 
             for (i = 0; i < ARRAY_CARDINALITY(kvmbins); ++i) {

src/util/util.c

@@ -1114,6 +1114,19 @@ char *virFindFileInPath(const char *file)
     char *pathseg;
     char fullpath[PATH_MAX];
 
+    if (file == NULL)
+        return NULL;
+
+    /* if we are passed an absolute path (starting with /), return a
+     * copy of that path
+     */
+    if (file[0] == '/') {
+        if (virFileExists(file))
+            return strdup(file);
+        else
+            return NULL;
+    }
+
     /* copy PATH env so we can tweak it */
     if (virStrcpyStatic(pathenv, getenv("PATH")) == NULL)
         return NULL;