testing, issue #1104: Make the test use static flags
Added version checker interface
inserted setUserAgent in each HTTP request
added APIVersion when call NewRegistry
Insert version checkers when call NewRegistry()
added client's kernel version
Removed an unnecessary error check.
Removed an unnecessary nil assignment
format in the user agent header should follow RFC 2616
reduce the number of string copy operations.
Packaging, issue #1174: Add pure binary to docker release
wip
Add verbose output to docker build

Verbose output is enabled by default and
the flag -q can be used to suppress the verbose output.
Fix buildfile tests after rebase
Revert changes from PR 1030

With streaming output of the build
changes in 1030 are no longer required.
Add param to api docs for verbose build output
Remove the os.user dependency and manually lookup /etc/passwd instead
updated the help commands on a few commands that were not correct
updated the rmi command docs, the had typos
Hack: use helper functions in tests for less copy-pasting