cleanup testcase
Expose several options from MockDirWrapper via index settings

Index settings can now override default behavior for 'double write'
and 'no delete open files' on MockDirectoryWrapper if tests use these
options in a legit. way. ie. in a restore situation a double write
is a legit operation.
Move Mock Store impls to test package
additional places not to do field conversions
serialize timestamp on the response
Catch RejectedExceutionException in ZenPing et al.

If nodes are shutting down we close thread pools and throw
'EsRejectedExcutionException'. This commit handles these exceptions
gracefully if throw during Ping execution.