Fail safely on invalid ScanResults when creating NetworkKey

Added tests for NetworkKey#createFromScanResult

Bug: 34671341
Test: runtest --path
frameworks/base/core/tests/coretests/src/android/net/NetworkKeyTest.java
runtest --path
frameworks/base/services/tests/servicestests/src/com/android/server/NetworkScoreServiceTest.java

Change-Id: Ideac1615917649cd3934421228a82aeed37e7ad1