networkValidate: Forbid new-line char in network name

networkValidate: Forbid new-line char in network name

New line character in name of network is now forbidden because it
mess virsh output and can be confusing for users.  Validation of
name is done in network driver, after parsing XML to avoid
problems with disappeared network which was already created with
new-line char in name.

Closes-Bug: https://bugzilla.redhat.com/show_bug.cgi?id=818064
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>