HMP: add infrastructure for sub command This patch make parsing of hmp command aware of that it may have sub command. Also discard simple encapsulation function monitor_find_command(). For case "@command ", space after @command is filtered out. Signed-off-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>