signup: added proper validation message for the password fields
signup: added proper validation message for the password fields

See bsc#1041905

Signed-off-by: Miquel Sabaté Solà <b4d70704b9e7df580cab34510621dbd0aacb2dfd@suse.com>

MaximilianMeister/velum,ereslibre/velum,kubic-project/velum,MaximilianMeister/velum,ereslibre/velum,ereslibre/velum,kubic-project/velum,vitoravelino/velum,MaximilianMeister/velum,ereslibre/velum,kubic-project/velum,vitoravelino/velum,kubic-project/velum,MaximilianMeister/velum,vitoravelino/velum,vitoravelino/velum