srm: Respect read-only session in 2.2 (equivalent of http://rb.dcache.org/r/5633/ for java 6 based 2.2)

This patch fixes the issues by attempting to failfast - fail SRM request even before the request handler is invoked and
there fore before requests are scheduled (in case of srmput). It is achieved by adding isReadOnly() method to SRMUser interface.

Ticket: 7842
Acked-by: Al Rossi
Target: 2.2
Bug: http://rt.dcache.org/Ticket/Display.html?id=7842
Request: 1.9.12
Require-book: no
Require-notes: yes

RELEASE NOTES
SRM respects read-only session qualifier (as specified in storage-authzb or dcache.kpwd). That is
if login record contains "read-only" qualifier SRM will refuse performing namespace modification
functions with SRM_AUTHORIZATION_FAILURE error code
Merge pull request #96 from DmitryLitvintsev/fix/2.2/readonlysrm

srm: Respect read-only session in 2.2 (equivalent of http://rb.dcache.or...