Fix some synchronisation issues in MasterService.cc.
Fix some synchronisation issues in MasterService.cc.

SMatsushi/RAMCloud,rstutsman/RAMCloud,anirajk/RAMCloud,Frank-Wu/RamCloud,utah-scs/RAMCloud,jblomer/ramcloud,utah-scs/RAMCloud,alexandermerritt/ramcloud,QingkaiLu/RAMCloud,mrdiegoa/ramcloud,jcarreira/ramcloud,utah-scs/RAMCloud,alexandermerritt/ramcloud,behnamm/cs244b_project,y-higuchi/ramcloud,rstutsman/RAMCloud,QingkaiLu/RAMCloud,SMatsushi/RAMCloud,mrdiegoa/ramcloud,y-higuchi/ramcloud,mrdiegoa/ramcloud,matrix207/RAMCloud,y-higuchi/ramcloud,utah-scs/RAMCloud,taschik/ramcloud-load-manager,IMCG/RamCloud,matrix207/RAMCloud,y-higuchi/ramcloud,matrix207/RAMCloud,jcarreira/ramcloud,alexandermerritt/ramcloud,DavidLi2010/ramcloud,jblomer/ramcloud,DavidLi2010/ramcloud,DavidLi2010/ramcloud,mrdiegoa/ramcloud,taschik/ramcloud-load-manager,QingkaiLu/RAMCloud,jblomer/ramcloud,SMatsushi/RAMCloud,Frank-Wu/RamCloud,Frank-Wu/RamCloud,IMCG/RamCloud,matrix207/RAMCloud,taschik/ramcloud,rstutsman/RAMCloud,rstutsman/RAMCloud,DavidLi2010/ramcloud,utah-scs/RAMCloud,behnamm/cs244b_project,taschik/ramcloud-load-manager,taschik/ramcloud-load-manager,QingkaiLu/RAMCloud,taschik/ramcloud,jcarreira/ramcloud,jcarreira/ramcloud,anirajk/RAMCloud,jblomer/ramcloud,SMatsushi/RAMCloud,alexandermerritt/ramcloud,behnamm/cs244b_project,taschik/ramcloud,Frank-Wu/RamCloud,SMatsushi/RAMCloud,alexandermerritt/ramcloud,rstutsman/RAMCloud,y-higuchi/ramcloud,IMCG/RamCloud,taschik/ramcloud-load-manager,DavidLi2010/ramcloud,QingkaiLu/RAMCloud,IMCG/RamCloud,jcarreira/ramcloud,anirajk/RAMCloud,behnamm/cs244b_project,taschik/ramcloud,jblomer/ramcloud,rstutsman/RAMCloud,matrix207/RAMCloud,mrdiegoa/ramcloud,anirajk/RAMCloud,alexandermerritt/ramcloud,jblomer/ramcloud,y-higuchi/ramcloud,Frank-Wu/RamCloud,taschik/ramcloud,mrdiegoa/ramcloud,jcarreira/ramcloud,Frank-Wu/RamCloud,QingkaiLu/RAMCloud,anirajk/RAMCloud,utah-scs/RAMCloud,DavidLi2010/ramcloud,matrix207/RAMCloud,behnamm/cs244b_project,IMCG/RamCloud,IMCG/RamCloud,SMatsushi/RAMCloud,behnamm/cs244b_project,anirajk/RAMCloud