tools/libxl: Improvements to libxl-save-helper when using valgrind

tools/libxl: Improvements to libxl-save-helper when using valgrind

Fix two unfree()'d allocations in libxl-save-helper, to get them out of the
way of other legitimate complaints from valgrind.

The first is easy; close the interface to libxc when done with it.

The second can be fixed by removing the complexity of creating the logging
instance.  Initialise the global 'logger' in place rather than as an
allocation, which requires changing the indirection of its use in 5 locations.

struct xentoollog_logger_tellparent and function createlogger_tellparent() are
now unused and removed.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>