check email and username before start installation

After some installation failure I found into django code how it validate email and username.

To be more consistent we can add this 2 check inside our installation script to avoid waste of time
during installation with wrong parameters.

import re

RE_VALID_USERNAME = re.compile('[\w.@+-]+$')

EMAIL_RE = re.compile(
    r"(^[-!#$%&'*+/=?^_`{}|~0-9A-Z]+(\.[-!#$%&'*+/=?^_`{}|~0-9A-Z]+)*" # dot-atom
    r'|^"([\001-\010\013\014\016-\037!#-\[\]-\177]|\\[\001-\011\013\014\016-\177])*"' # quoted-string
    r')@(?:[A-Z0-9-]+\.)+[A-Z]{2,6}$', re.IGNORECASE) # domain

def is_valid_email(value):
    if not EMAIL_RE.search(value):
        raise exceptions.ValidationError(_('Enter a valid e-mail address.'))

if not RE_VALID_USERNAME.match(username):
                raise CommandError("Invalid username. Use only letters, digits, and underscores")