MINOR: stick-table: Add prefixes to stick-table names.

MINOR: stick-table: Add prefixes to stick-table names.

With this patch we add a prefix to stick-table names declared in "peers" sections
concatenating the "peers" section name followed by a '/' character with
the stick-table name. Consequently, "peers" sections have their own
namespace for their stick-tables. Obviously, these stick-table names are not the
ones which should be sent over the network. So these configurations must be
compatible and should make A and B peers communicate with peers protocol:

    # haproxy A config, old way stick-table declerations
    peers mypeers
        peer A ...
        peer B ...

    backend t1
        stick-table type string size 10m store gpc0 peers mypeers

    # haproxy B config, new way stick-table declerations
    peers mypeers
        peer A ...
        peer B ...
        table t1 type string size store gpc0 10m

This "network" name is stored in ->nid new field of stktable struct. The "local"
stktable-name is still stored in ->id.