Address code review feedback

Also make sure we copy the joining containers hosts and resolv.conf with
the hostname if we are joining it's network stack.
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Merge pull request #5569 from vieux/add__ping_to_the_API

Add  ping to the api
Merge pull request #5496 from unclejack/check_if_root

check if the daemon is run as root on startup
import sha512 to make sha512 ssl certs work

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Merge pull request #5591 from alexlarsson/fix-expose-parsing

nat: Fix --expose protocol parsing
Add alex as devmapper and btrfs maintainer
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
cgroups: Update systemd to match fs backend

This updates systemd.Apply to match the fs backend by:
* Always join blockio controller (for stats)
* Support CpusetCpus
* Support MemorySwap

Also, it removes the generic UnitProperties in favour of a single
option to set the slice.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Check supplied hostname before using it.

Docker-DCO-1.1-Signed-off-by: Rohit Jnagal <jnagal@google.com> (github: rjnagal)
Merge pull request #5544 from vieux/cleanup_api_client

Cleanup api client
Improve libcontainer namespace and cap format
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
It's its.
Merge pull request #5580 from tianon/update-vendor-versions

Update vendored deps that have a proper version number to use said specific versions
Merge pull request #5604 from nirvdrum/patch-1

It's its.
Merge pull request #5400 from bmatsuo/5398-fix-pkg/graphdb-osx
Merge pull request #5596 from dotcloud/contrib-fix

Post-commit hook URL fix
Merge pull request #5538 from shykes/pr_out_engine_catchall_handler_is_shadowed_by_specific_handlers
Merge pull request #5575 from vieux/pr-5428
Merge pull request #5602 from crosbymichael/libcontainer-enable

Improve libcontainer namespace and cap format
Merge pull request #4441 from crosbymichael/add-net-flag

Add --net flag to docker run and allow host network stack
Update after namespace refactor
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)