[FAB-2214] 1st block in chain is block 0, not 1
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>