[NAN] Method renames based on API council feedback

- Fix tenses throughout
- connect -> attach
- disconnect/terminate -> destroy
- IsUsable -> IsAvailable

Note: pure rename operation - no functional changes

(cherry-pick of commit 34a0342a)

Bug: 31470256
Test: unit tests + integration (sl4a) test
Change-Id: I0f275c590c63109b7196622cfc5001082e3eb5a2