streamchain

Made the following changes to fsblkstorage provider:

* Block numbers start at 0, not 1.

* Blockchain height should be last block number + 1.

* A block's Block.Header.Number should be equal to
  the Blockchain height when AddBlock() is called.

* Updated ledger tests to use random temporary dir.

* Update core endorser tests to generate valid block
  numbers.

Change-Id: I0208cd6a4b9da462c29d06126fa651f4c0dcd2fc
Signed-off-by: Luis Sanchez <sanchezl@us.ibm.com>