Credential storage triggers unlock when keystore is locked.

If the phone is in the unlocked state and keystore is locked, storing
credentials asks for a password that does not exist to the user. Replace
this workflow with a key guard confirmation, asking the user to unlock
the screen in the same way they would normally unlock their phone.

Bug: 68298609
Test: adb push sample_credentials.p12 /sdcard/
Test: adb shell su 1000 service call android.security.keystore 9 i32 0
Test: adb shell am start -a android.credentials.INSTALL --user 10
Test: adb shell su 1000 service call android.security.keystore 9 i32 10

Change-Id: I8a3068a5d7de508fb417016acdf41b1712a2e7cc