tools: xen-access: Check return values and clean up on errors during init

tools: xen-access: Check return values and clean up on errors during init

Check the return values of the libxc mem_access calls.  Free allocated
structures (platform_info, domain_info) on errors during
initialization and exit.  Unbind VIRQ, close event channel and
connection to Xen on errors during initialization

Signed-off-by: Aravindh Puthiyaparambil <aravindh@virtuata.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>