[xen-tools] hook scripts issue, and patch

Hello,

I've recently run into problems because of the way the hook scripts
define functions and evaluates expressions.

By default on Ubuntu Edgy, dash is installed, and /bin/sh is a symlink
to dash. The xen-tools hook scripts use the keyword "function" for
function definitions, and [[ ]] for expression evaluation. These are
*not* supported by dash. This makes the hook scripts fail with errors
like this:

Running hook 99-clean-image
['/usr/lib/xen-tools/dapper.d/99-clean-image /tmp/NWz3ScGIho']
--
/usr/lib/xen-tools/common.sh: 19: function: not found
/tmp/NWz3ScGIho
/usr/lib/xen-tools/common.sh: 51: function: not found
/usr/lib/xen-tools/common.sh: 77: logMessage: not found
assert failed: /usr/lib/xen-tools/dapper.d/99-clean-image: []

The attached patch fixes the problem by not using the "function"
keyword for function definition and by using [ expression ] instead of
[[ expression ]] for expression evaluation in the hook shell scripts.
In this way the hook shell scripts work whether /bin/sh is a symlink
to /bin/bash or to /bin/dash.

Patch applies to current CVS.

Thanks,
-- 
Eric