admin.py: added command to add suites

Syntax:

s add SUITE VERSION [ label=LABEL ] [ description=DESCRIPTION ]
                    [ origin=ORIGIN ] [ codename=CODENAME ]
                add suite SUITE, version VERSION. label,
                description, origin and codename are optional.

SUITE and VERSION are mandatory.  LABEL, DESCRIPTION, ORIGIN and
CODENAME can be optionally passed in a keyword-parameter-style
(var=value).

Signed-off-by: Mario Domenech Goulart <mario@ossystems.com.br>