Always use the server based provider if HAL isn't installed

If the device doesn't have the reboot escorw HAL, default the provider
to server-based. It helps OEM testing before our P/H flag rollout;
because most OEM devices don't install the HAL.

Test: unittests
Change-Id: Ia43ab0abb769bbf8e11e61841f4a647ae2acc6be