Add ability to install credentials as other UID

We need the ability to install from the system UID to wifi UID
to explicitly bind WiFi credentials to the WiFi profile. This adds the
ability for Wifi Settings to invoke installation of a PKCS12 file for
the wifi UID.

Bug: 8183258
Change-Id: I357c4387baf7e2f6fd6acc9046d9e6b52fdd4bb0