add metastore, switching sequence to use it

metastore is for storing metadata. This will be used later when moving
to distributed master mode.

go/metastore/memory_backing.go

@@ -0,0 +1,37 @@
+package metastore
+
+import (
+	"fmt"
+	"path"
+)
+
+//this is for testing only
+
+type MetaStoreMemoryBacking struct {
+	m map[string][]byte
+}
+
+func NewMetaStoreMemoryBacking() MetaStoreMemoryBacking {
+	mms := MetaStoreMemoryBacking{}
+	mms.m = make(map[string][]byte)
+	return mms
+}
+
+func (mms MetaStoreMemoryBacking) Set(val []byte, elem ...string) error {
+	mms.m[path.Join(elem...)] = val
+	return nil
+}
+
+func (mms MetaStoreMemoryBacking) Get(elem ...string) (val []byte, err error) {
+	var ok bool
+	val, ok = mms.m[path.Join(elem...)]
+	if !ok {
+		return nil, fmt.Errorf("Missing value for %s", path.Join(elem...))
+	}
+	return
+}
+
+func (mms MetaStoreMemoryBacking) Has(elem ...string) (ok bool) {
+	_, ok = mms.m[path.Join(elem...)]
+	return
+}