v.io/x/ref: Modify Seekblessings to not close tab if browser=false
v.io/x/ref: Modify Seekblessings to not close tab if browser=false

The alternative is to add a new flag called autoclose that defaults
to true. This way is simpler.

I think it makes sense to reuse the browser flag because:
- if the tab was opened automatically, it should close automatically
- if the tab had to be opened manually, it should be closed manually

Change-Id: Ie1dc73b40870febc57019375c142b910d78ff11c

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref