Update Provider installation in tests

Change CertPinManagerTest and CTVerifierTest to only install the
provider if it's not installed already and check if the provider was
installed before uninstalling.  Otherwise, they will uninstall the
platform copy of Conscrypt and break every following test.

Bug: 124428935
Test: cts -m CtsLibcoreTestCases -t com.android.org.conscrypt
Change-Id: I8c4f11e9898007c7456d95d8d825dabdf50651e1