Fixed the issue with echo command in port mapping isolator.

sh: echo: I/O error occurs, It is not possible to set the port range.
Also, echo in /bin/sh performs output a (horizontal) tab character
when encountered the escape sequence of \t.

Review: https://reviews.apache.org/r/28904
Added multiplication and division operators for Bytes.

Review: https://reviews.apache.org/r/28983
Split apart the Bytes test.

Review: https://reviews.apache.org/r/28984
Updated Resources interface to expose reservations.

Review: https://reviews.apache.org/r/28985
Removed Resources::extract in favor of reservation-based helpers.

Review: https://reviews.apache.org/r/28986
Added an allocator unit test for allocatable resources.

Review: https://reviews.apache.org/r/28987
Fixed the two level sorting in the allocator.

Review: https://reviews.apache.org/r/28824