Let tests enumerate all transports/capabilities.

This gives them a way to collect all included values without
resorting to manual probing of each newly added value.

Cherry-pick of ag/4052941 with minor conflicts in the imports.

Bug: 16207332
Test: atest com.android.cts.net.HostsideVpnTests
Change-Id: Ia764b3412bf834890612378e0c3846913f4e0a06
Merged-In: Ie5cd22cfa2b6a60510fd1e31d7ebcd8f6cc890a0
Merged-In: If07e77c92046807235229a4f67ee087bdd7bccf1