nfsv4: some operation must be solo in the compound

CREATE_SESSION, DESTROY_CLIENTID and EXCHANGE_ID

fixes sone test cases from pynfs testsuite

Acked-by: Gerd Behrmann
Target: master
nfsv4: DESTROY_CLIENTID must return BUSY on existing sessions

fixes test case from pynfs testsuite

Acked-by: Gerd Behrmann
Target: master
nfsv: fix client principal for non GSS credentials

NFSv4.1 spec enforces gss security, but in real life AUTH_SYS is used.
fixes test case from pynfs testsuite

Acked-by: Gerd Behrmann
Target: master
nfsv4: open_owner clientid used for v4.0 only

Acked-by: Gerd Behrmann
Target: master