Enable docker container related tests for linux ppc64le

The current docker - container related jtreg tests only run on linux x86_64; change tests + test infrastructure so that linux ppc64le (little endian PowerPC) is also supported.
Docker runs on linuxppc64le as well.
While testing on SLES12 / linux ppc64le it turned out that the parsing of /proc/self/cgroup and /proc/self/mountinfo in osContainer_linux.cpp had to be adjusted (not sure if this is a SLES issue or a ppc64le issue). We parsed in the files for "cpu,cpuacct" entries but on SLES12 they showed up as "cpuacct,cpu", so both version needed to be considered.