Improve bash completion for ulimits

[albers]

- What I did

Several Docker commands have options to create/run a container with special ulimits.
These options take an individual limit as their argument, e.g. nofile=100.
Before this PR, bash completion had no special support for these arguments, treating them as "any string".

See #2712 for the recently added support for ulimits in services.
This change extends the completion part of #2712 and therefore should go into the same Docker release.

- How I did it

Added bash completion for the individual limits after --ulimit|--ulimit-add|ulimit-rm|default-ulimit.

- How to verify it

$ docker service create --ulimit <TAB><TAB>
as=            cpu=           locks=         memlock=       nofile=        rss=           stack=
chroot=        data=          maxlogins=     msgqueue=      nproc=         rtprio=
core=          fsize=         maxsyslogins=  nice=          priority=      sigpending=

$ docker service update --ulimit-add <TAB><TAB>
as=            cpu=           locks=         memlock=       nofile=        rss=           stack=
chroot=        data=          maxlogins=     msgqueue=      nproc=         rtprio=
core=          fsize=         maxsyslogins=  nice=          priority=      sigpending=

$ docker service update --ulimit-rm <TAB><TAB>
as            cpu           locks         memlock       nofile        rss           stack
chroot        data          maxlogins     msgqueue      nproc         rtprio
core          fsize         maxsyslogins  nice          priority      sigpending

$ docker create --ulimit <TAB><TAB>
as=            cpu=           locks=         memlock=       nofile=        rss=           stack=
chroot=        data=          maxlogins=     msgqueue=      nproc=         rtprio=
core=          fsize=         maxsyslogins=  nice=          priority=      sigpending=

$ docker run --ulimit <TAB><TAB>
as=            cpu=           locks=         memlock=       nofile=        rss=           stack=
chroot=        data=          maxlogins=     msgqueue=      nproc=         rtprio=
core=          fsize=         maxsyslogins=  nice=          priority=      sigpending=

$ docker build --ulimit <TAB><TAB>
as=            cpu=           locks=         memlock=       nofile=        rss=           stack=
chroot=        data=          maxlogins=     msgqueue=      nproc=         rtprio=
core=          fsize=         maxsyslogins=  nice=          priority=      sigpending=

$ dockerd --default-ulimit <TAB><TAB>
as=            cpu=           locks=         memlock=       nofile=        rss=           stack=
chroot=        data=          maxlogins=     msgqueue=      nproc=         rtprio=
core=          fsize=         maxsyslogins=  nice=          priority=      sigpending=

- Description for the changelog

Improved bash completion for ulimits

[codecov-commenter]

Codecov Report

Merging #2714 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2714   +/-   ##
=======================================
  Coverage   58.59%   58.59%           
=======================================
  Files         296      296           
  Lines       21360    21360           
=======================================
  Hits        12516    12516           
  Misses       7931     7931           
  Partials      913      913           

[thaJeztah]

nice! LGTM thank you!

[thaJeztah]

@silvin-lubecki PTAL

[silvin-lubecki]

LGTM, thanks a lot @albers 👍