[Opm] Libecl upgrade required

[Joakim Hove]

[ Sorry if you have already recieved this - I had some problems sending it
from the Equinor account. ]


Tomorrow morning I intend to merge this PR:
https://github.com/Statoil/libecl/pull/538 in libecl - that must/will be
merged syncronously with this: https://github.com/OPM/opm-common/pull/575
in opm-common; so after this you will need to pull an updated libecl to
build opm-common.


Joaim