NM was requiring that bond slaves have either no IP config or an
explicit "none"/"disabled" config. But the system scripts just ignore
any IP config that is present on a slave, so change NM to do that too
(but warn about it).
https://bugzilla.redhat.com/show_bug.cgi?id=838907
Single quotes ensure we don't break initscripts (bash processing) when the
string contains special characters. Special handling is necessary for single
quotes characters. They have to be escaped and the whole string has to be
prepended with '$' character so that bash is happy.
This change also filters out CR and LF characters as they break WPA_PSK
variable and could pose security issues.
