Since Pike release, Cinder supports volume online extending, and by
default it assumes that every backend supports this feature. This
assumption causes a bug on those backends that don't support it. On
such backends, an online extending attempt leaves the volume in
error_extending state.
This patch allows a backend to report to the scheduler if it does not
support online extending. This way, an online extending attempt will
fail, without leaving the volume in error_extending state.
Closes-bug: #1765182
Change-Id: I2c31b5c171574074a8fc7ba86f94f983fc9658f7
Co-Authored-By: Lucio Seki <luciomitsuru.seki@fit-tecnologia.org.br>