Tests should tolerate cpusets. (#1853)
Tests should tolerate cpusets. (#1853)

Motivation:

Our current CPU pinning tests do not expect to be pinned to cores that
do not include core 0. That's unnecessary.

Modifications:

- Expect to pin to the first core in our cpuset.

Result:

Tests run inside cpusets.
apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio