Fix for mesos fetcher not applying the executor bit.

Review: https://reviews.apache.org/r/21127
Updated tests to use a strict registry, by default.

Review: https://reviews.apache.org/r/20820
Enabled unbundled usage of http-parser.

Updates libprocess configure check for http-parser to build against
system dependencies outlined in MESOS-1071 + fixes libprocess local
'make check' which was broken.

Review: https://reviews.apache.org/r/20983