Adds Oakmore Labs to Mesos adopters documentation.
Reorganized authentication implementation locations.

For paving the way into further authentication mechanism
implementations, the existing is reorganized.

Move src/sasl to src/authentication/cram_md5.
Rename src/tests/sasl_tests.cpp to src/tests/cram_md5_authentication_tests.cpp.
Adapt depending include paths.
Rename specific test implementations from SASL to CRAMMD5Authentication.
Rename sasl namespace to cram_md5 throughout all uses.
Add missing license blob to auxprop.cpp.

Review: https://reviews.apache.org/r/27122
Added CRAM-MD5 Test Authenticator module.

Introducing the CRAM-MD5 SASL test authenticator module based on the
former sasl/authenticator.

The former sasl/authenticator.hpp still remains as part of libmesos but
now is located at authentication/cram_md5.

Review: https://reviews.apache.org/r/26857
Integrated CRAM-MD5 Authenticator module.

Enables selecting a module based authenticator via the new
--authenticators flag for mesos master.

Additionally, all "> >" have been fixed towards ">>" in master.hpp and
master.cpp.

Review: https://reviews.apache.org/r/26859
Integrated CRAM-MD5 Authenticator module into tests.

The CRAM-MD5 authenticator module is now usable via mesos-tests.sh

Example usage:
bin/mesos-tests.sh \
--authenticators=org_apache_mesos_TestCRAMMD5Authenticator \
--modules="{\"libraries\": [{\"file\": \
\"src/.libs/libtestauthenticator.so\",\"modules\": [{\"name\": \
\"org_apache_mesos_TestCRAMMD5Authenticator\"}]}]}"

Review: https://reviews.apache.org/r/26860
Minor fix to balloon framework test.
Updated Modules protobuf to simplify JSON parsing.

Updates the --modules help messages accordingly.

Review: https://reviews.apache.org/r/27481
Updated --isolation help message for slave.

Now also mentions the --modules flag.

Review: https://reviews.apache.org/r/27560
First version of docs/modules.md.

With bits copied from
https://cwiki.apache.org/confluence/display/MESOS/Mesos+Modules+Developer+Guide.

Review: https://reviews.apache.org/r/27453
Update release guide to mention configure.ac.
Adds GoCardless to Mesos adopters list.
Pass user into Isolator::prepare.

Review: https://reviews.apache.org/r/27557
Permit unprivileged executors to created child cgroups.

MesosContainerizer Isolators using cgroups will chown the cgroup to
the executor user, if specified, enabling the executor to create child
cgroups. Cgroup control files are not chowned so the executor cannot
modify its own cgroups, only control files for child cgroups.

Review: https://reviews.apache.org/r/27558
Fix OsTest.killtreeNoRoot check for reparenting.

Reparenting does not always assign to pid 1 (/sbin/init). If there is
a user init such as init --user with some other pid, this will be the
new parent.

Modify os_tests to check that the subtree has been reparented to a
process different from its original parent (a.k.a. child) and that it
is not a zombie.

Review: https://reviews.apache.org/r/27461
Documentation for filesystem/shared isolator.

Review: https://reviews.apache.org/r/27584
Documentation for namespaces/pid isolator.

Review: https://reviews.apache.org/r/27585
Updated release guide to mention configuration.md.

To update the flags for master, slave and configure.

Review: https://reviews.apache.org/r/27573
Add source and reason to TaskStatus.

Review: https://reviews.apache.org/r/26382/
Add MESOS-343 and MESOS-1143 to CHANGELOG.

Review: https://reviews.apache.org/r/27595/
Add destroy tests for docker containerizer.