The checkers and stressers should be composable without special cases; this
patch tries to address that while refactoring out some old cruft.
Namely,
* Single stresser/checker for a tester; built from composition
* Composite stresser via comma-separated list of stressers
* Split stressers into separate files
* Removed v2 only flags and special cases
* Rate limiter shared among key stresser and leases stresser
* Composite checker is now concurrent
* Stresser can return a Checker to check its invariants
* Each lease checker only operates on a single lease stresser
These really belong in tester code; the stressers and
checkers are higher order operations that are orchestrated
by the tester. They're not really cluster primitives.
This commit adds a new option -failure-wrapper to etcd-tester. The
option receives a path of script that is used for enabling/disabling
external fault injectors. The script is called with an option "enable"
when it needs to be enabled (when failure.Inject() is called) and
called with "disabled" in an opposite case (when failure.Recover() is
called).
This commit adds a new option --failures to etcd-tester. The option
receives a comma-delimited argument like this:
"default,failpoints". The given arguments are interpreted as names of
failures and they are injected to an etcd cluster. Available failures
are default (default scenario in etcd-tester) and failpoints. If no
args are passed to the option (--failures=""), no failures are
injected during testing.
