Document in which version new types and functions were added using
".. versionadded:: x.y". Document changes using
".. versionchanged:: x.y."
For watchdog module, add the versionadded tag in the module top
docstring, not on each type/function.
Add docstring to ssh_execute().
I used "git blame" + "git tag --contains=SHA1" to find these version,
and then I checked manually each version.
Change-Id: I56a7d8a4335833e9b49eedab026d20adfeedf942
e01418018f