xl: Suppress spurious warning message for cpupool-list

xl: Suppress spurious warning message for cpupool-list

libxl_cpupool_list() enumerates the cpupools by "probing": calling
cpupool_info, starting at 0 and stopping when it gets an error. However,
cpupool_info will print an error when the call to xc_cpupool_getinfo() fails,
resulting in every xl command that uses libxl_list_cpupool (such as
cpupool-list) printing that error message spuriously.

Since at the moment the times we want to print the message correspond
with the use of the existing "exact" parameter, use it to decide
whether to print the message or not.

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>