tty: set the handle to blocking mode

Checklist

• tests and code linting passes
• a test and/or benchmark is included
• documentation is changed or added
• the commit message follows commit guidelines

Affected core subsystem(s)

tty, process

Description of change

See discussion at:

• https://github.com/nodejs/node/pull/177#issuecomment-119351671
• https://github.com/nodejs/node/issues/6456#issuecomment-219620603
• https://github.com/nodejs/node/pull/6773

cc @nodejs/ctc @isaacs @ksc @saghul etc

Note: we still have more investigation to do but this is looking like it is probably the correct thing to do.