Do not cache rkp_only property

To allow for testing, read the rkp_only properties every time instead
of caching the value. This allows the RemoteProvisioner tests to alter
the property, moving the device in and out of rkp-only mode.

Test: RemoteProvisionerUnitTests
Bug: 27306369
Change-Id: If9a616fd36095175f4aea07c897c67a11eb04bcf
1 file changed