[NAN] Method renames based on API council feedback [DO NOT MERGE]

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

Note: pure rename operation - no functional changes

Bug: 31470256
Test: unit tests + integration (sl4a) test
Change-Id: I9d150cc2e00d5d95d27c9671d728c21e4488f5b8