Don't remove existing EAP configurations

When merging backed-up configurations with the current supplicant
configuration, we read both configurations into a instance of
WifiNetworkSettings.  No EAP configurations should be restored as
per b/25725016, however existing EAP configurations that already
reside in wpa_supplicant.conf (presumably configured in SUW)
should not be removed in the process.

This CL adds a parameter to the "readNetworks" method to allow it
to select whether or not EAP configurations should be read in.  It
is used to allow the "restoreWifiSupplicant" method to copy in EAP
configurations from the existing wpa_supplicant.conf, but not out
of the backup data.

BUG: 28873992
Change-Id: I8b3e0c1a6629b3f1ca5055b1b2190e6b3ca4c033