Handle ETIMEDOUT during socket connection

[blaknite]

This fixes #161 in which we failed to rescue Errno::ETIMEDOUT errors from our socket connection during test runs. This would cause the test run to complete with a non-zero exit code and cause build jobs to fail.

This is the error that is now rescued:

bundler: failed to load command: rspec (.../ruby/2.7.0/bin/rspec)
Traceback (most recent call last):
	2: from .../ruby/2.7.0/gems/buildkite-test_collector-1.2.5/lib/buildkite/test_collector/socket_connection.rb:69:in `block in initialize'
	1: from .../lib/ruby/2.7.0/openssl/buffering.rb:125:in `readpartial'
.../lib/ruby/2.7.0/openssl/buffering.rb:125:in `sysread': Operation timed out (Errno::ETIMEDOUT)

I was able to reproduce the error by disabling my wifi mid run as reported in the issue. This PR fixes the bug under the same conditions.

[niceking]

lol I love that you disabled your wifi for this 😂