Small Ubuntu 15.10 docker image

The size of this image is less than 56MB (more than half of ubuntu:15.10). This is possible by the removal of packages that are not required in a container:

• dmsetup
• e2fsprogs
• init
• initscripts
• libcap2-bin
• libcryptsetup4
• libdevmapper1.02.1
• libkmod2
• libsmartcols1
• libudev1
• mount
• procps
• systemd
• systemd-sysv
• tzdata
• udev
• util-linux
• bash