Wrong Error Message When Number Contains two "-" symbols Before a Number

[LeoNerdoG]

If you add two minus symbols before a number in min length password field, Kapua report that a number is too big, although you add e.g. --15.

Testflow:

1. Login as kapua-sys
2. Go to Accounts, create an account (e.g. acco0)
3. Select acc0, go to Account settings, change password.min.lenght to --15
4. Observe the error

Expected behavior
Error message should be different (e.g. negative values not allowed or something similar).

Screenshots

Version of Kapua
[e.g. 1.0.0]

Type of deployment
[ ] Local Vagrant deployment
[ ] Docker
[ ] Openshift (in its variants)
[ ] Others

Main component affected
[ ] Console (in case of console please report info on which browser you encountered the problem)
[ ] REST API
[ ] Message Broker
[ ] - Others

Additional context
Add any other context about the problem here.

[lorthirk]

As per #15, it's not a trivial task to add more validation logic on configuration fields. We will evaluate it for a later release.