ARM-CI : Check a device is already mounted while mounting a device.
ARM-CI : Check a device is already mounted while mounting a device.

Now ARM-CI makes building failure frequently with below messages.

http://dotnet-ci.cloudapp.net/job/dotnet_corefx/job/master/job/linuxarmemulator_cross_release/127/console
19:21:33 + unmount_rootfs /opt/linux-arm-emulator-root/dev
19:21:33 + local rootfsFolder=/opt/linux-arm-emulator-root/dev
19:21:33 + grep -qs /opt/linux-arm-emulator-root/dev /proc/mounts
19:21:33 + sudo umount /opt/linux-arm-emulator-root/dev
umount: /opt/linux-arm-emulator-root/dev: device is busy.
19:21:33         (In some cases useful info about processes that use
19:21:33          the device is found by lsof(8) or fuser(1))
19:21:33 Build step 'Execute shell' marked build as failure

I suggest though the script is exited by any cases, the script would not run un-mounting.
But whenever CI is running and mounting a device, It will check the device is already mounted.

I think this error is occurred from the script of running tests. I hope to resolve this problem As soon as possible.
In before resolving this problem, It would rather apply it than errors are occurred.

dotnet-bot/corefx,dhoehna/corefx,gkhanna79/corefx,lggomez/corefx,elijah6/corefx,nbarbettini/corefx,ravimeda/corefx,dhoehna/corefx,krytarowski/corefx,mazong1123/corefx,rjxby/corefx,rubo/corefx,ViktorHofer/corefx,zhenlan/corefx,the-dwyer/corefx,rubo/corefx,richlander/corefx,krk/corefx,yizhang82/corefx,alphonsekurian/corefx,ericstj/corefx,Jiayili1/corefx,krytarowski/corefx,shmao/corefx,krk/corefx,fgreinacher/corefx,jlin177/corefx,MaggieTsang/corefx,Petermarcu/corefx,Petermarcu/corefx,cydhaselton/corefx,yizhang82/corefx,marksmeltzer/corefx,Petermarcu/corefx,fgreinacher/corefx,ericstj/corefx,weltkante/corefx,BrennanConroy/corefx,yizhang82/corefx,parjong/corefx,ptoonen/corefx,krytarowski/corefx,DnlHarvey/corefx,Jiayili1/corefx,zhenlan/corefx,yizhang82/corefx,parjong/corefx,nbarbettini/corefx,zhenlan/corefx,alphonsekurian/corefx,krytarowski/corefx,alphonsekurian/corefx,richlander/corefx,lggomez/corefx,billwert/corefx,billwert/corefx,YoupHulsebos/corefx,marksmeltzer/corefx,JosephTremoulet/corefx,ravimeda/corefx,parjong/corefx,alexperovich/corefx,nbarbettini/corefx,JosephTremoulet/corefx,nbarbettini/corefx,rjxby/corefx,dotnet-bot/corefx,ravimeda/corefx,jlin177/corefx,mmitche/corefx,MaggieTsang/corefx,YoupHulsebos/corefx,billwert/corefx,rahku/corefx,fgreinacher/corefx,dotnet-bot/corefx,ptoonen/corefx,mmitche/corefx,shimingsg/corefx,rjxby/corefx,YoupHulsebos/corefx,axelheer/corefx,ptoonen/corefx,elijah6/corefx,yizhang82/corefx,parjong/corefx,rubo/corefx,ericstj/corefx,shimingsg/corefx,stephenmichaelf/corefx,stephenmichaelf/corefx,stone-li/corefx,Petermarcu/corefx,marksmeltzer/corefx,krk/corefx,krytarowski/corefx,elijah6/corefx,zhenlan/corefx,richlander/corefx,BrennanConroy/corefx,krk/corefx,parjong/corefx,zhenlan/corefx,nbarbettini/corefx,dotnet-bot/corefx,nchikanov/corefx,tijoytom/corefx,zhenlan/corefx,richlander/corefx,Ermiar/corefx,twsouthwick/corefx,seanshpark/corefx,Jiayili1/corefx,krytarowski/corefx,nchikanov/corefx,ViktorHofer/corefx,gkhanna79/corefx,seanshpark/corefx,cydhaselton/corefx,nchikanov/corefx,billwert/corefx,mazong1123/corefx,rahku/corefx,ptoonen/corefx,Ermiar/corefx,DnlHarvey/corefx,MaggieTsang/corefx,DnlHarvey/corefx,weltkante/corefx,stone-li/corefx,dotnet-bot/corefx,MaggieTsang/corefx,nchikanov/corefx,JosephTremoulet/corefx,ericstj/corefx,stone-li/corefx,twsouthwick/corefx,lggomez/corefx,cydhaselton/corefx,mazong1123/corefx,seanshpark/corefx,axelheer/corefx,weltkante/corefx,the-dwyer/corefx,JosephTremoulet/corefx,alphonsekurian/corefx,ptoonen/corefx,rahku/corefx,JosephTremoulet/corefx,Petermarcu/corefx,krk/corefx,shmao/corefx,Ermiar/corefx,twsouthwick/corefx,tijoytom/corefx,zhenlan/corefx,YoupHulsebos/corefx,MaggieTsang/corefx,nbarbettini/corefx,cydhaselton/corefx,ViktorHofer/corefx,mazong1123/corefx,Jiayili1/corefx,MaggieTsang/corefx,rjxby/corefx,rubo/corefx,twsouthwick/corefx,stone-li/corefx,cydhaselton/corefx,gkhanna79/corefx,axelheer/corefx,YoupHulsebos/corefx,wtgodbe/corefx,rahku/corefx,rjxby/corefx,axelheer/corefx,ravimeda/corefx,ViktorHofer/corefx,Ermiar/corefx,ravimeda/corefx,stone-li/corefx,the-dwyer/corefx,gkhanna79/corefx,rjxby/corefx,mazong1123/corefx,YoupHulsebos/corefx,Petermarcu/corefx,jlin177/corefx,seanshpark/corefx,the-dwyer/corefx,mazong1123/corefx,alphonsekurian/corefx,twsouthwick/corefx,elijah6/corefx,MaggieTsang/corefx,parjong/corefx,gkhanna79/corefx,dotnet-bot/corefx,krk/corefx,ravimeda/corefx,lggomez/corefx,lggomez/corefx,tijoytom/corefx,alphonsekurian/corefx,rjxby/corefx,weltkante/corefx,elijah6/corefx,stone-li/corefx,dhoehna/corefx,mmitche/corefx,alexperovich/corefx,ViktorHofer/corefx,ptoonen/corefx,Petermarcu/corefx,parjong/corefx,krytarowski/corefx,weltkante/corefx,the-dwyer/corefx,stone-li/corefx,ViktorHofer/corefx,wtgodbe/corefx,mazong1123/corefx,shmao/corefx,dhoehna/corefx,alexperovich/corefx,ptoonen/corefx,rubo/corefx,dhoehna/corefx,shimingsg/corefx,elijah6/corefx,shmao/corefx,jlin177/corefx,yizhang82/corefx,alexperovich/corefx,rahku/corefx,mmitche/corefx,DnlHarvey/corefx,stephenmichaelf/corefx,gkhanna79/corefx,richlander/corefx,tijoytom/corefx,tijoytom/corefx,nchikanov/corefx,mmitche/corefx,weltkante/corefx,nchikanov/corefx,shimingsg/corefx,gkhanna79/corefx,rahku/corefx,shimingsg/corefx,seanshpark/corefx,billwert/corefx,stephenmichaelf/corefx,shimingsg/corefx,dhoehna/corefx,nchikanov/corefx,axelheer/corefx,cydhaselton/corefx,twsouthwick/corefx,alexperovich/corefx,elijah6/corefx,seanshpark/corefx,DnlHarvey/corefx,tijoytom/corefx,axelheer/corefx,BrennanConroy/corefx,tijoytom/corefx,alphonsekurian/corefx,shmao/corefx,marksmeltzer/corefx,twsouthwick/corefx,marksmeltzer/corefx,richlander/corefx,shimingsg/corefx,marksmeltzer/corefx,JosephTremoulet/corefx,rahku/corefx,alexperovich/corefx,stephenmichaelf/corefx,cydhaselton/corefx,Jiayili1/corefx,ericstj/corefx,stephenmichaelf/corefx,jlin177/corefx,dhoehna/corefx,fgreinacher/corefx,Ermiar/corefx,shmao/corefx,dotnet-bot/corefx,yizhang82/corefx,billwert/corefx,wtgodbe/corefx,ViktorHofer/corefx,seanshpark/corefx,nbarbettini/corefx,wtgodbe/corefx,lggomez/corefx,DnlHarvey/corefx,Ermiar/corefx,weltkante/corefx,wtgodbe/corefx,the-dwyer/corefx,billwert/corefx,lggomez/corefx,the-dwyer/corefx,jlin177/corefx,Ermiar/corefx,Jiayili1/corefx,mmitche/corefx,krk/corefx,alexperovich/corefx,YoupHulsebos/corefx,wtgodbe/corefx,jlin177/corefx,JosephTremoulet/corefx,ericstj/corefx,ericstj/corefx,shmao/corefx,wtgodbe/corefx,ravimeda/corefx,richlander/corefx,Jiayili1/corefx,mmitche/corefx,marksmeltzer/corefx,DnlHarvey/corefx,stephenmichaelf/corefx