BUG/MINOR: cli: allow space escaping on the CLI

BUG/MINOR: cli: allow space escaping on the CLI

It was not possible to escape spaces over the CLI, making impossible the
insertion of new ACL entries with spaces from the CLI.

This patch fixes the escaping of spaces over the CLI.

It is now possible to launch "add acl agents.acl My\ User\ Agent" over
the CLI.

Could be backported in all stable branches.

Should fix issue #400.

(cherry picked from commit b08c6d06e712b148bf396dcf13f7da590a6104c9)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>