docker daemon: show info about the server

For combing through logs, have an intro line with information about the
running instance of the docker daemon.

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
Fix a few minor man formatting consistency issues

Some flags ended with a colon, some didn't.  For man pages, the prevailing normal practice is not to end the flags lines with colons.

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Update bundlescripts to use "set -e" consistently

"set -e" is already inherited here from make.sh, but explicit is always better than implicit (hence the "set -e" in the first place!)

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Avoid "invalid memory address or nil pointer dereference" panic

libcontainer.GetNamespace returns nil on FreeBSD because
libcontainer.namespaceList is empty. In this case, Namespaces#Get should
return nil instead of being panic.

Docker-DCO-1.1-Signed-off-by: Kato Kazuyoshi <kato.kazuyoshi@gmail.com> (github: kzys)
net: do not create -b/--bridge specified bridge

If the bridge specified using -b/--bridge doesn't
exist, fail instead of attempting to create it.

This is consistent with the docker documentation
on -b/--bridge: "Attach containers to a pre
existing network bridge". 

It is also less surprising in an environment where
the operator expected the bridge to be properly
set up before docker starts and expects docker to
fail fast if the bridge was not up instead of
masking this error and coming up in some
potentially broken state.

With this patch, docker still creates docker0 if
needed and no bridge was explicitly specified.

Docker-DCO-1.1-Signed-off-by: Daniel Norberg <daniel.norberg@gmail.com> (github: danielnorberg)
bridge driver: clean up error returns

Docker-DCO-1.1-Signed-off-by: Daniel Norberg <daniel.norberg@gmail.com> (github: danielnorberg)
Merge pull request #5143 from kzys/ns-nil

Avoid "invalid memory address or nil pointer dereference" panic
Merge pull request #4990 from vbatts/vbatts-server_show_info

docker daemon: show info about the server
Merge pull request #5093 from danielnorberg/do-not-create-bridge

net: do not create -b/--bridge specified bridge
Merge pull request #5071 from tianon/minor-man-formatting-consistency

Fix a few minor man formatting consistency issues
Merge pull request #5072 from tianon/hack-set-e-consistently

Update bundlescripts to use "set -e" consistently