LU-10070 lod: SEL: Add FLR support

LU-10070 lod: SEL: Add FLR support

Add FLR support for self-extending layouts.

The basic model is that when a layout intent would modify
an FLR replica, we first run the extent_update code to
perform any layout extent changes for self extending
layouts.

This treats the FLR operations (stale, resync, etc)
similarly to i/o, creating initialized layout where those
operations need it.  This makes the interaction between SEL
and FLR fairly simple.

Add FLR tests for self-extending layouts

Cray-bug-id: LUS-2528
Signed-off-by: Patrick Farrell <paf@cray.com>
Change-Id: Ia23df8e226955f64e9b19df993b66d2d4f820f33
Reviewed-on: https://review.whamcloud.com/33785
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>