Add HasValidGITPrefix to utils/utils.go

This will allow us to use a common Git prefix check for both api/clients/commands.go and
builder/job.go. Previous prefix check in build from Git (in builder/jobs.go) ignored valid prefixes such as "git@", "http://" or "https://".

Signed-off-by: Lakshan Perera <lakshan@laktek.com>
adding support for port ranges on --expose
Closes #1834

Signed-off-by: Srini Brahmaroutu <srbrahma@us.ibm.com>
Reword a sentence bringing confusion about docker links

As [discovered][1] doing user support, the sentence `You've learned that a link creates a
source container that can provide information about itself to a recipient container` brings
confusion.

[1]: http://stackoverflow.com/questions/26652877/how-to-avoid-redundant-container-linking-in-docker-when-propagating-ip-addresses/26654203?noredirect=1#comment41945048_26654203

Signed-off-by: Thomas LEVEIL <thomasleveil@gmail.com>
Merging MalteJ:set-macaddress

Signed-off-by: Malte Janduda <mail@janduda.net>
Adding IPv6 support to docker daemon

Signed-off-by: Malte Janduda <mail@janduda.net>