common/cgroup: add mountFsRO() helper function
common/cgroup: add mountFsRO() helper function

There are some places in the common/cgroup/cgroup.go which contain the same
code which collects flags to mount a filesystem in read-only mode and calls
mount system call with the given flags and a filesystem source/target.

This patch adds mountFsRO() helper function to prevent code duplication.

Signed-off-by: Alexander Kuleshov <1e54dc1c299571bb7a58e37a7ea31ffd91d38f4e@gmail.com>

yifan-gu/rocket,nhlfr/rkt,jakon89/rkt,coreos/rkt,achanda/rkt,Shashwatsh/rkt,nhlfr/rkt,coreos/rkt,squeed/rkt,dgonyeo/rkt,shobhit85/rkt,alban/rkt,coreos/rkt,jjlakis/rkt,squeed/rkt,nhlfr/rkt,sstabellini/rkt,sgotti/rkt,jakon89/rkt,jonboulle/rkt,yifan-gu/rkt,jakon89/rkt,rkt/rkt,joshix/rkt,joshix/rkt,alban/rkt,Shashwatsh/rkt,joshix/rkt,jonboulle/rkt,Wilybald/rkt,Wilybald/rkt,ybubnov/rkt,squeed/rkt,ybubnov/rkt,s-urbaniak/rkt,monstermunchkin/rkt,rkt/rkt,Wilybald/rkt,euank/rkt,intelsdi-x/rkt,lucasallan/rkt,Wilybald/rkt,sstabellini/rkt,akshaykarle/rkt,kinvolk/rkt,shobhit85/rkt,yifan-gu/rocket,akshaykarle/rkt,lucasallan/rkt,yifan-gu/rocket,s-urbaniak/rkt,lucasallan/rkt,joshix/rkt,kinvolk/rkt,intelsdi-x/rkt,Shashwatsh/rkt,kinvolk/rkt,s-urbaniak/rkt,monstermunchkin/rkt,rkt/rkt,akshaykarle/rkt,jjlakis/rkt,monstermunchkin/rkt,jjlakis/rkt,intelsdi-x/rkt,sstabellini/rkt,jonboulle/rkt,ybubnov/rkt,rkt/rkt,cab105/rkt,alban/rkt,cab105/rkt,kinvolk/rkt,shobhit85/rkt,euank/rkt,yifan-gu/rkt,cab105/rkt,achanda/rkt,dgonyeo/rkt,euank/rkt,sgotti/rkt,achanda/rkt,lucasallan/rkt,dgonyeo/rkt,sgotti/rkt,yifan-gu/rkt