DPM: API review for installKeyPair

Per API council review, make installKeyPair take a single, integer flags
argument rather than two boolean ones.

Bug: 71818124
Test: cts-tradefed run commandAndExit cts-dev -a armeabi-v7a -m CtsDevicePolicyManagerTestCases -t com.android.cts.devicepolicy.DeviceOwnerTest#testKeyManagement -l DEBUG
Change-Id: Ia04f8d617ae0d1db028bd9bcef3a4bf486449468