block/gluster: improve defense over string to int conversion

block/gluster: improve defense over string to int conversion

using atoi() for converting string to int may be error prone in case if
string supplied in the argument is not a fold of numerical number,

This is not a bug because in the existing code,

static QemuOptsList runtime_tcp_opts = {
    .name = "gluster_tcp",
    .head = QTAILQ_HEAD_INITIALIZER(runtime_tcp_opts.head),
    .desc = {
        ...
        {
            .name = GLUSTER_OPT_PORT,
            .type = QEMU_OPT_NUMBER,
            .help = "port number ...",
        },
...
};

port type is QEMU_OPT_NUMBER, before we actually reaches atoi() port is already
defended by parse_option_number()

However It is a good practice to use function like parse_uint_full()
over atoi() to keep port self defended

Note: As now the port string to int conversion has its defence code set,
and also we understand that port argument is actually a string type,
in the follow up patch let's move port type from QEMU_OPT_NUMBER to
QEMU_OPT_STRING

[Jeff Cody: removed spurious parenthesis]

Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>