archipelago: Introduce ArchipelagoPoolClient class

The class can be instantiated without any argument, the default
configuration file which is used is '/etc/archipelago/archipelago.conf':

    pool = ArchipelagoPoolClient()

or using another configuration file:

    pool = ArchipelagoPoolClient(conffile='local.conf')

or using another connection endpoint for the connection pooler:

    pool = ArchipelagoPoolClient(endpoint='poold.socket')

    or

    pool = ArchipelagoPoolClient(conffile='local.conf',
                                 endpoint='poold.socket')

or using a set of keyword arguments describing the full segment
characteristics:

    pool = ArchipelagoPoolClient(segtype='posix', segname='archipelago',
                                 dynports=1024, ports=2048, segsize=2048,
                                 segalign=12)

The basic segment parameters are:

- *segname*: the segment name
- *segtype*: the segment type
- *dynports*: the dynamic ports range
- *ports*: the total ports range
- *segsize*: the segmen size
- *segalign*: the segment alignment

Any other keyword parameter will be passed to the underlying client
libraries: the list of supported parameters depends on the library version.

The following functionality is provided:

- Connect to connection pooler

    pool.connect()

- Get an Archipelago port

    portctx = pool.get_port()

- Return Archipelago port back to connection pool

    pool.leave_port(portctx)

- Check if connection is alive

    pool.alive()

- Return all ports the instatiated object holds back to the connection pool

    pool.leave_all_ports()

Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>