Using validator "SnmpPassword" into SNMP Password Entry

Previously miss validations for SNMP password to check it
without spaces and at least 8 chars.
Now add validator "SnmpPassword" into SNMP Password Entry

Change-Id: I3b58ee0776eab2c2e540206ef04f357b24544acc
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=984450
Signed-off-by: hadong <hadong0720@gmail.com>