Check if repository is a mount and not just a directory
Check if repository is a mount and not just a directory

Summary:
Renaming a repository fails when repositories are mount points.
I don't fully understand what moving the directory is supposed to accomplish, but this should work

Test Plan: I tested on Sandcastle using BTRFS

Reviewed By: alexander-ponomarenko, dorserg

fbshipit-source-id: 6eccf51

brettwooldridge/buck,k21/buck,robbertvanginkel/buck,brettwooldridge/buck,LegNeato/buck,shybovycha/buck,dsyang/buck,LegNeato/buck,facebook/buck,shybovycha/buck,dsyang/buck,robbertvanginkel/buck,brettwooldridge/buck,k21/buck,ilya-klyuchnikov/buck,brettwooldridge/buck,shs96c/buck,SeleniumHQ/buck,zpao/buck,ilya-klyuchnikov/buck,SeleniumHQ/buck,k21/buck,romanoid/buck,dsyang/buck,LegNeato/buck,JoelMarcey/buck,rmaz/buck,k21/buck,dsyang/buck,vschs007/buck,clonetwin26/buck,shybovycha/buck,Addepar/buck,marcinkwiatkowski/buck,rmaz/buck,shybovycha/buck,vschs007/buck,SeleniumHQ/buck,shs96c/buck,dsyang/buck,rmaz/buck,nguyentruongtho/buck,dsyang/buck,JoelMarcey/buck,nguyentruongtho/buck,dsyang/buck,zhan-xiong/buck,k21/buck,JoelMarcey/buck,SeleniumHQ/buck,romanoid/buck,shs96c/buck,kageiit/buck,zhan-xiong/buck,brettwooldridge/buck,nguyentruongtho/buck,ilya-klyuchnikov/buck,robbertvanginkel/buck,Addepar/buck,vschs007/buck,shs96c/buck,clonetwin26/buck,zpao/buck,ilya-klyuchnikov/buck,JoelMarcey/buck,LegNeato/buck,vschs007/buck,dsyang/buck,dsyang/buck,Addepar/buck,marcinkwiatkowski/buck,clonetwin26/buck,romanoid/buck,shybovycha/buck,brettwooldridge/buck,shs96c/buck,marcinkwiatkowski/buck,k21/buck,robbertvanginkel/buck,facebook/buck,zhan-xiong/buck,romanoid/buck,zhan-xiong/buck,rmaz/buck,Addepar/buck,zpao/buck,rmaz/buck,LegNeato/buck,Addepar/buck,zpao/buck,Addepar/buck,LegNeato/buck,zhan-xiong/buck,zpao/buck,kageiit/buck,shybovycha/buck,clonetwin26/buck,LegNeato/buck,marcinkwiatkowski/buck,SeleniumHQ/buck,brettwooldridge/buck,shs96c/buck,ilya-klyuchnikov/buck,vschs007/buck,ilya-klyuchnikov/buck,shybovycha/buck,romanoid/buck,LegNeato/buck,rmaz/buck,romanoid/buck,facebook/buck,brettwooldridge/buck,shs96c/buck,SeleniumHQ/buck,JoelMarcey/buck,ilya-klyuchnikov/buck,zhan-xiong/buck,ilya-klyuchnikov/buck,zhan-xiong/buck,SeleniumHQ/buck,k21/buck,Addepar/buck,rmaz/buck,LegNeato/buck,rmaz/buck,marcinkwiatkowski/buck,ilya-klyuchnikov/buck,SeleniumHQ/buck,kageiit/buck,clonetwin26/buck,romanoid/buck,robbertvanginkel/buck,JoelMarcey/buck,k21/buck,SeleniumHQ/buck,rmaz/buck,JoelMarcey/buck,Addepar/buck,k21/buck,robbertvanginkel/buck,zhan-xiong/buck,vschs007/buck,JoelMarcey/buck,zhan-xiong/buck,zpao/buck,LegNeato/buck,clonetwin26/buck,LegNeato/buck,romanoid/buck,vschs007/buck,brettwooldridge/buck,clonetwin26/buck,JoelMarcey/buck,Addepar/buck,kageiit/buck,ilya-klyuchnikov/buck,nguyentruongtho/buck,nguyentruongtho/buck,brettwooldridge/buck,shs96c/buck,JoelMarcey/buck,vschs007/buck,clonetwin26/buck,ilya-klyuchnikov/buck,marcinkwiatkowski/buck,shs96c/buck,shybovycha/buck,shs96c/buck,dsyang/buck,facebook/buck,shybovycha/buck,rmaz/buck,facebook/buck,zhan-xiong/buck,LegNeato/buck,vschs007/buck,ilya-klyuchnikov/buck,marcinkwiatkowski/buck,kageiit/buck,SeleniumHQ/buck,robbertvanginkel/buck,clonetwin26/buck,marcinkwiatkowski/buck,kageiit/buck,shs96c/buck,robbertvanginkel/buck,romanoid/buck,k21/buck,dsyang/buck,marcinkwiatkowski/buck,Addepar/buck,ilya-klyuchnikov/buck,Addepar/buck,Addepar/buck,k21/buck,clonetwin26/buck,facebook/buck,rmaz/buck,zhan-xiong/buck,vschs007/buck,marcinkwiatkowski/buck,romanoid/buck,robbertvanginkel/buck,romanoid/buck,kageiit/buck,robbertvanginkel/buck,zhan-xiong/buck,dsyang/buck,rmaz/buck,nguyentruongtho/buck,shybovycha/buck,marcinkwiatkowski/buck,nguyentruongtho/buck,romanoid/buck,clonetwin26/buck,marcinkwiatkowski/buck,shs96c/buck,marcinkwiatkowski/buck,brettwooldridge/buck,robbertvanginkel/buck,shs96c/buck,brettwooldridge/buck,shybovycha/buck,k21/buck,vschs007/buck,shybovycha/buck,robbertvanginkel/buck,romanoid/buck,shybovycha/buck,JoelMarcey/buck,dsyang/buck,Addepar/buck,SeleniumHQ/buck,zpao/buck,vschs007/buck,clonetwin26/buck,LegNeato/buck,k21/buck,JoelMarcey/buck,SeleniumHQ/buck,JoelMarcey/buck,zhan-xiong/buck,vschs007/buck,SeleniumHQ/buck,rmaz/buck,robbertvanginkel/buck,facebook/buck,brettwooldridge/buck,clonetwin26/buck