Separate namespace acquisition from library loading

This way native bridge namespace could be acquired in advance and when
library must be loaded JNIEnv is not needed.

Bug: http://b/79940628

Test: cts-tradefed run commandAndExit cts -m CtsGpuToolsHostTestCases

Change-Id: If8bff272fc5245eb4e418807c3bdd29e82833ab8