Support mallinfo() statistics on Linux/glibc systems via agent

[mblauth]

In some scenarios it might be interesting to get statistics about glibc arena use etc. Maybe it would be possible to extract that data via an agent from the target vm.

[mblauth]

mallinfo() support was added. mallinfo2() support was skipped for the time being as the glibc for the current use case doesn't have it. Before closing the issue we should implement it. Additionally we should clearly communicate the shortcomings of these calls (see respective manpages),