Fix lustre version parsing

[ofaaland]

These two commits re-work how lmt handles differences in the location and contents of the Lustre version file for Lustre <= 2.8 vs. > 2.8.

The first commit reverts

• 8a2a19c Add /sys in Lustre version checking (#31) which causes lmt to always look in the real /proc or /sys to find the lustre version, which ultimately breaks the compatability tests performed via "make check".

The second commit alters _read_lustre_version_string() to correctly handle the contents of the Lustre version file after v 2.8 (a bare version string) as well as up to v 2.8 (3 rows in key-value format).

Testing: Tested by hand with "make check", running utils/ltop on a cluster running lmt-3.2.6 and another one running lmt-3.2.7, and running lmtmetric on an MDS and OSS on lustre servers running lustre 2.10.8.

Fixes #49

[ofaaland]

Merged

• f984897 handle lustre version file containing bare version
• 91c9c9d Revert "Add /sys in Lustre version checking (#31)"