commandserver: get around ETIMEDOUT raised by selectors2
selector.select() should exits with an empty event list on timed out, but
selectors2 raises OSError if timeout expires while recovering from EINTR.
Spotted while debugging new chg feature.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}