image.sh: Updates to image-attach

Apparently usleep is a RH specific thing.  Use it if it exists; otherwise,
use sleep.

Also, since xl block-attach often fails while returning success, check to make
sure the requested block device actually exists.

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
core: Default dry_run to false

This got lost when we moved away from gwd_testlib.sh

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
image.sh: Fix a syntax error

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
tblib: Add help for tb-make-{image,config}, normalize directory names

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
guestlib: Make vm-vnc work again

Use host_addr if no host is set.

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
tblib: Add backendtype to help

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
guestlib: Fix path for arplog-get-ip.

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>