Bug 1227: Removed #close() from Write Transactions.

Bug 1227: Removed #close() from Write Transactions.

Termination of write transactions was unclear due
to several terminal methods such as commit, cancel
and close.

Close was removed from write transactions and is only
available for read-only transactions.

Termination methods for write transactions are close
 and commit.

Introduced new interfaces for ReadOnly transactions
to clearly distinguish between read capability
of transaction and read-only semantic (which has
close method).

Change-Id: I74b3fd2066a55160da3b674156fc0dc54ba14a67
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>