call validation when creating/editing Provider URL for Network Provider

added call to validate connection details when testing settings from
ProviderModel.

Change-Id: I0b9e9a6b66d800c973334629fa34b3b5443290df
Bug-Url: https://bugzilla.redhat.com/1111974
Signed-off-by: Martin Mucha <mmucha@redhat.com>