Secret keys are not longer identifiable by their alias prefix.
So now we call getKeyCharacteristics and check the algorithm of the
key.
Bug: 63931634
Test: Manually installed a key and checked that it is still dispayed
correctly.
Change-Id: I55a4e46434618cb52ceb9456f184e004165872fd
Deleting wifi certificates isn't supported yet since cascading the
removal back into wifi configs will need some easy way of enumerating
wifi configs first.
Bug: 29208062
Change-Id: I2d9d1ea7e0974701009bfa6ea162b8bc80806639