qmp-shell converts only integer arguments and the rest
is assumed to be strings which are faithfully sent as
quoted strings by json. But QEMU refuses to accept qmp
command with boolean argument whose value is escaped
as string.

Fix it by special-casing true/false keywords and store
value as corresponding boolean.
Signed-off-by: NIgor Mammedov <imammedo@redhat.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>