host: Switch use of json decoder to terser use of Unmarshal.

Signed-off-by: Eric Myhre <eric@flynn.io>
host: style: Golang convention is to have initialisms fully capitalized.

Signed-off-by: Eric Myhre <eric@flynn.io>
host: go fmt

Signed-off-by: Eric Myhre <eric@flynn.io>
host: Add cleanup of host state persistence db handles to tests.

This doesn't affect correctness, but it's messy to leave file handles open for no reason.

Signed-off-by: Eric Myhre <eric@flynn.io>
host: Whitespace police.

Signed-off-by: Eric Myhre <eric@flynn.io>
host: Remove stateFileMtx from host state.  Use of boltdb has its own internal locking mechanisms which obviate the need for this mutex.

Signed-off-by: Eric Myhre <eric@flynn.io>