ProcFSTools: implement conforming parse_mounts

There are a few places where we grep over /proc/mounts
without taking the encoding into acount.
ProcFSTools::parse_mounts parses mount data and decodes all
the special character the kernel might encode into it.

Shortcut: parse_proc_mounts to do
parse_mounts(read_proc_mounts()).
is_mounted() updated to parse mounts correctly.