[FAB-2603] Change & export dir containing ledgers

https://jira.hyperledger.org/browse/FAB-2603

1. Ledgers were maintained as directories inside a "blocks" directory.
Semantically speaking, this doesn't quite make sense -- you'd expect to
find blocks under a "blocks" directory.

2. The name of this directory should be an exported constant so that
other packages can access it programmatically. The orderer package for
instance, needs this info in order to construct the proper directories
for its ledger.

This changeset addresses both of these issues.

Change-Id: I3bdf9763e227c29983003bab0769282136a42511
Signed-off-by: Kostas Christidis <kostas@christidis.io>

common/ledger/blkstorage/fsblkstorage/config.go

@@ -19,7 +19,11 @@ package fsblkstorage
 import "path/filepath"
 
 const (
-	defaultMaxBlockfileSize = 64 * 1024 * 1024
+	// ChainsDir is the name of the directory containing the channel ledgers.
+	ChainsDir = "chains"
+	// IndexDir is the name of the directory containing all block indexes across ledgers.
+	IndexDir                = "index"
+	defaultMaxBlockfileSize = 64 * 1024 * 1024 // bytes
 )
 
 // Conf encapsulates all the configurations for `FsBlockStore`
@@ -38,13 +42,13 @@ func NewConf(blockStorageDir string, maxBlockfileSize int) *Conf {
 }
 
 func (conf *Conf) getIndexDir() string {
-	return filepath.Join(conf.blockStorageDir, "index")
+	return filepath.Join(conf.blockStorageDir, IndexDir)
 }
 
-func (conf *Conf) getBlocksDir() string {
-	return filepath.Join(conf.blockStorageDir, "blocks")
+func (conf *Conf) getChainsDir() string {
+	return filepath.Join(conf.blockStorageDir, ChainsDir)
 }
 
 func (conf *Conf) getLedgerBlockDir(ledgerid string) string {
-	return filepath.Join(conf.getBlocksDir(), ledgerid)
+	return filepath.Join(conf.getChainsDir(), ledgerid)
 }

common/ledger/blkstorage/fsblkstorage/fs_blockstore_provider.go

@@ -56,7 +56,7 @@ func (p *FsBlockstoreProvider) Exists(ledgerid string) (bool, error) {
 
 // List lists the ids of the existing ledgers
 func (p *FsBlockstoreProvider) List() ([]string, error) {
-	return util.ListSubdirs(p.conf.getBlocksDir())
+	return util.ListSubdirs(p.conf.getChainsDir())
 }
 
 // Close closes the FsBlockstoreProvider