This fix tries to address the issue raised in 24596 where it was not
possible to join as manager only (`--availability=drain`).
This fix adds a new flag `--availability` to `swarm join`.
Related documentation has been updated.
An integration test has been added.
NOTE: Additional pull request for swarmkit and engine-api will
be created separately.
This fix fixes 24596.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
Upstream-commit: ab2635ead0
Component: cli
7d950520e5