Don't use -o argument to "free"

The /bin/free on Fedora 21 doesn't understand -o argument to free;
that being:

---
 -o, --old
   Display the output in old format, the only difference being this
   option will disable the display of the "buffer adjusted" line.
---

i.e. the difference is the "-/+ buffers/cache" line.  Since the sed
only matches on the line starting "^Mem", this is not relevant anyway.

Change-Id: Ib2f763ea82b9a3b397d202453099d58e5dd5a355
Merge "Don't use -o argument to "free""