Use argv0 as reexec implementation for dockerinit

This changes the way the exec drivers work by not specifing a -driver
flag on reexec.  For each of the exec  drivers they register their own
functions that will be matched aginst the argv 0 on exec and called if
they match.

This also allows any functionality to be added to docker so that the
binary can be reexec'd and any type of function can be called.  I moved
the flag parsing on docker exec to the specific initializers so that the
implementations do not bleed into one another.  This also allows for
more flexability within reexec initializers to specify their own flags
and options.

Signed-off-by: Michael Crosby <michael@docker.com>
Remove unsued sysinit package

Signed-off-by: Michael Crosby <michael@docker.com>
Fix hack in old integration test for new init

Signed-off-by: Michael Crosby <michael@docker.com>
Add "DEBIAN_FRONTEND" to FAQ

Added some explanation on using ‘DEBIAN_FRONTEND’ to the FAQs. As
discussed here;
https://github.com/docker/docker/pull/7035#issuecomment-50967867

Docker-DCO-1.1-Signed-off-by: Sebastiaan van Stijn <github@gone.nl> (github: thaJeztah)
Merge pull request #7516 from thaJeztah/faqs-explain-debian-noninteractive

Add "DEBIAN_FRONTEND" to FAQ
Add test case for identical short and long version numbers

Signed-off-by: Lajos Papp <lajos.papp@sequenceiq.com>
Fix equal short-long version number comparison

Signed-off-by: Lajos Papp <lajos.papp@sequenceiq.com>
Private Repos Copy Change

Docker-DCO-1.1-Signed-off-by: Christopher Biscardi <biscarch@sketcht.com> (github: ChristopherBiscardi)
tell the user what to expect, including that it is a verbode process.

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@docker.com> (github: SvenDowideit)
Merge pull request #7398 from SvenDowideit/add-more-details-to-https-docs

tell the user what to expect, including that it is a verbose process.
Panic if trying to register an func with the same name

Signed-off-by: Michael Crosby <michael@docker.com>
Merge pull request #7490 from crosbymichael/reexec

Use argv0 as reexec implementation for dockerinit
Updates docs regarding linux mint troubleshot

Signed-off-by: Ciro S. Costa <ciro.costa@usp.br>
Merge pull request #7533 from cirocosta/patch-1

Updates docs regarding linux mint troubleshot
Merge pull request #7531 from ChristopherBiscardi/priv-repos

Private Repos Copy Change
Merge pull request #7528 from lalyos/fix_version_number_comparison

Fix version number comparison
Add irc-meetings section in CONTRIBUTING

Signed-off-by: Tibor Vass <teabee89@gmail.com>
Merge pull request #7466 from tiborvass/irc-meetings

Add irc-meetings section in CONTRIBUTING