MB-13633 Allocate memory segment for key in multi KVS mode
MB-13633 Allocate memory segment for key in multi KVS mode

- Since there is 8-byte prefix in front of key in multi KVS mode,
we should not directly use doc->key given by user for reading
document from file.

Change-Id: I2a0b06b593d32f3218766b2ff4d4db2eab827a96

zhaog/forestdb,joliss/forestdb,hisundar/forestdb,sushmaad/forestdb,hisundar/forestdb,wurikiji/forestdb,sushmaad/forestdb,couchbase/forestdb,yyangpan/forestdb,wurikiji/forestdb,nvoron23/forestdb,joliss/forestdb,jinxuan/forestdb,yyangpan/forestdb,couchbase/forestdb,seem-sky/forestdb,jinxuan/forestdb,seem-sky/forestdb,nvoron23/forestdb,zhaog/forestdb