Work around LVM related race condition when using --force with LVM

If an "lvremove" is immediately followed by an "lvcreate" for an LV
with the same name, "mkswap" (and maybe other commands) occasionally
fail with "Device or resource busy".

Work around it by using sync and sleep.

bin/xen-create-image

@@ -3066,6 +3066,10 @@ sub createLVMBits
                     logprint(
                         "Removing $lvm_disk - since we're forcing the install\n");
                     runCommand("lvremove --force $lvm_disk", \%CONFIG);
+                    runCommand("sync", \%CONFIG);
+                    logprint(
+                        "Sleeping a few seconds to avoid LVM race conditions...\n");
+                    sleep(3);
                 } else {
                     fail("ERROR: Xen guest $CONFIG{'hostname'} appears to be running.\nAborting.\n");
                 }